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Vol. 8. Issue 3.
Pages 2481-3388 (May - June 2019)
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Vol. 8. Issue 3.
Pages 2481-3388 (May - June 2019)
Original Article
DOI: 10.1016/j.jmrt.2017.06.014
Open Access
An Al–7Si alloy/cast iron bimetallic composite with super-high shear strength
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Zhilin Guoa, Min Liub,
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mliu@sdu.edu.cn

Corresponding authors.
, Xiufang Biana,
Corresponding author
xfbian@sdu.edu.cn

Corresponding authors.
, Meijia Liuc, Jianguo Lid
a Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061, China
b School of Civil Engineering, Shandong University, Jinan 250061, China
c School of Materials Science and Engineering, University of Jinan, Jinan 250022, China
d School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
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Tables (6)
Table 1. Reports on the shear property of Al/Fe bimetallic composites in literatures.
Table 2. The composition of cast iron and Al–7 Si alloy (wt.%).
Table 3. Experiment parameters of hot-dipping Zn–Bi melt.
Table 4. The compositions (at.%) detected by EDS at red-color 1–9 site in Fig. 2.
Table 5. Hot-dip parameters of the hot-dipping Zn–Bi melt and the control groups of another three hot-dipping melts.
Table 6. The detailed information on the microstructure of Al/Fe bonding interface in Fig. 2.
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Abstract

A new composite technology is presented consisting of the surface pretreatment of cast irons, the hot-dipping in a Zn–0.2wt.% Bi melt and the Al/Fe composite process. The shear strength of Al/Fe (Al–7Si/cast iron) bimetallic composites fabricated by the technology is up to 32MPa that is far more than the shear property obtained by composite technology reported in literatures. The super-high shear strength is mainly attributed to the formation of a peculiar concave–convex interface (CCI) structure. The addition of 0.2wt.% bismuth into the zinc melt can promote the formation of Zn-rich regions at the surface layer of cast irons, leading to the formation of Al–Fe phases at these Zn-rich regions. Reducing the amount of Al–Fe phases appearing in the ferrite–graphite interface in cast irons can benefit improving the shear property of Al/Fe bonding interface. Further analysis of the stress state confirms that the CCI can enhance the shear strength of Al/Fe bonding interface.

Keywords:
Al–7Si alloy
Cast iron
Hot-dipping
Shear strength
Bimetallic
Interface
Full Text
1Introduction

The situation that involves energy waste, emission pollution induced by the lower energy efficiency of automobiles impels researchers to focus on fabricating automobiles with lightweight, better fuel-economy and less fume emissive properties [1,2]. One innovation in the automobile industry is proposed that is to use a multi-material as car body structure for reducing the automotive deadweight [3–7]. Al/Fe bimetallic composites, as one of the multi-material series, have a good combination of both high strength, wear resistance from the Fe (cast irons/steels) and high heat conductivity, corrosion resistance and lightweight properties from the Al (pure Al/aluminum alloys). They have attracted an extensive attention on the applications in automobile body, such as engine blocks [8,9] and pistons [10] etc. However, the greater physicochemical differences between the Al and the Fe restrict the large-scale applications of Al/Fe bimetallic composites in the automobile body. For example, the Al melt wettability of cast irons is easily weakened because of a solder melt oxidation [11], leading to the difficulty of triggering the metallurgical reaction of Al/Fe [12]. The thicker rich-Al phase (Al3Fe, Al5Fe2) layer [13] or the thinner total Al–Fe phase layer [1] can generate a great threat to the bonding property of Al/Fe composite interface. Thus, during the manufacture process there are still some challenges on how to obtain a sound metallurgical bonding, even a better interface shear property, by overcoming physicochemical differences between Al and Fe [14].

Although lots of methods at the laboratory scale have been developed in present to join Al with Fe, such as friction stir welding (FSW) [15–17], laser welding–brazing (LWB) [18–20], cold metal transfer (CMT) [21,22], rolling [23,24] and riveting [25], these methods are applied difficultly to join complex-shape components [1]. Composite casting technique that can combine liquid metals with solid metals by a solid–liquid metallurgical reaction has a great flexibility of joining complex-shape components [26] (Fig. 1). For example, Liu et al. [27] developed a new composite casting method characterized by hot-dipping in Zn–2.2wt.% Al melt to obtain a metallurgical bonding of aluminum alloys/mild steels. Furthermore, most of methods including the above [15–25] are mainly focused on joining aluminum alloys with steel. Methods of connecting aluminum alloys and gray cast iron are rarely reported.

Fig. 1.

(a) Engine block with four cylinders. (b) The image of cross-section of engine block in image (a). (c) The magnification image from red rectangle in image (b).

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Increasing interface shear property plays a positive role in the application of Al/Fe bimetallic composites in automobiles. However, a limited number of literatures have an investigation on optimizing interfacial shear property of Al/Fe bimetallic composites, and the improved shear strength value is not very high. Jiang et al. [28] investigated the effects of surface pretreatments to steel on the shear property of Al/Fe (aluminum alloy/mild steel) bonding interface, and reported that the improved interfacial shear strength reached 10.4MPa. Sun et al. [29] reported that the improved shear strength of Al/Fe (aluminum alloy/casting iron) bonding interface reached 19.53MPa. Contrast to the already reported shear property of Al/Fe bimetallic composites in literatures [28–30], the shear property obtained by our technology is far more than that, as shown in Table 1.

Table 1.

Reports on the shear property of Al/Fe bimetallic composites in literatures.

Al/Fe matrix  Shear strength  Researcher  Literature 
ZL114 A/mild steel  10.4MPa  W. Jiang et al.  [18] 
Aluminum alloy/austenitic cast iron  19.53MPa  L. Sun et al.  [19] 
AS 13 alloy/mild steel  10MPa  O. Dezellus et al.  [30] 
ZL 101/HT 250  32MPa  Z.L. Guo et al.  This work 

In this work, a new composite casting technology is developed consisting of the surface pretreatment of cast irons, the hot-dipping in Zn–Bi (Zn–0.2wt.% Bi) melt, the Al/Fe composite process to obtain an Al/Fe (Al–7Si alloy/casting iron) bimetallic composite with super-high shear strength. Relationships between the super-high shear strength and the interface microstructure were investigated with comparison to hot-dipping in Al–7.2wt.% Si melts (from [24]), pure Zn melts, and Zn–2.2wt.% Al melts (from [31]). The effect of interface morphology on the shear property of Al/Fe bimetallic composites was also investigated. Finally, the further analysis on the stress state of Al/Fe bonding interface was shown to account for the effect of interfacial morphology on interface shear property.

2Materials and methods2.1Materials

The cast iron (Table 2) stripes of 4mm×9mm×75mm were prepared by using wire cut equipment to cut engine block cylinders. The Al–7Si alloy (Table 2) placed in the crucible was melt by medium-frequency induction furnace, acting as the liquid matrix of liquid/solid composite system. The Zn–0.2wt.% Bi alloy used as coating alloy was prepared by adding bismuth (99.99wt.%) into the pure zinc (99.95wt.%) melt during the heating of medium-frequency induction furnace, and then was charged into the resistance furnace to keep the temperature at 753±5K for 15min at least.

Table 2.

The composition of cast iron and Al–7 Si alloy (wt.%).

  Si  Mn  Mg  Al  Fe 
Cast iron  3.16–3.30  1.79–1.93  0.89–1.04  0.09–0.12  0.12–0.17  –  –  Bal 
Al–7Si alloy  –  6.5–7.5  –  –  –  0.2–0.4  Bal  – 
2.2Methods2.2.1Hot-dipping and Al/Fe composite process

Prior to the Al/Fe composite process, the cast iron stripe as Fe matrix needs to be coated with Zn–Bi (Zn–0.2wt.% Bi) alloy and then is connected with Al–7Si alloy. The major process is as follows: firstly, Zn–Bi melt in a crucible was enough stirred mechanically before immersing the Fe matrix into the hot-dipping melt at a bath temperature of 753±5K for 120s (Table 3). Then, Fe matrix was extracted from the Zn–Bi melt at the speed of 1.5m/min [32] and put into the mold at 453±10K. Finally, Al–7Si alloy melt (in Table 2) was poured immediately onto the Zn–Bi coating cladded Fe matrix in the mold at 453±10K. After the above steps, the Al/Fe bimetallic composites were then cooled to the ambient temperature in air. The hot dipping processes were then repeated as the schedule in Table 3.

Table 3.

Experiment parameters of hot-dipping Zn–Bi melt.

Hot-dipping times (s)  Hot-dipping temperature (K)
120±753±10  793±10  833±10  873±10 
180±753±10  793±10  833±10  873±10 
240±753±10  793±10  833±10  873±10 
480±753±10  793±10  833±10  873±10 
600±753±10  793±10  833±10  873±10 
2.2.2Characterizations of the mechanical properties and the microstructure of Al/Fe bimetallic composites

For the convenience of testing and detection, Al/Fe bimetallic composites were cut into specimens of 5mm×7mm×20mm in the wire cut equipment. The shear strength of Al/Fe bimetallic composite from each group of parameters in Table 3 was the average value of shear strength from using five specimens. The width of Al/Fe reaction layer was measured by optical microscopy. The scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS) was used to analyze the microstructure and the morphology of Al/Fe bonding layer. Al/Fe intermetallic phases in the bonding interface were detected by X-ray diffraction (XRD) analysis on the fracture surface of the Al/Fe composite specimens.

3Results3.1Microstructure and shear strength of Al/Fe bimetallic composites produced by hot-dipping in Al–7.2wt.% Si alloy melt, pure Zn melt, Zn–2.2wt.% Al melt, Zn–0.2wt.% Bi melt

We conducted the EDS analyses (Table 4) on the Al/Fe composite interface shown in Fig. 2(a)–(d). XRD analyses (Fig. 3) were also performed in order to further make certain the constitution of intermetallic phases in Al/Fe composite interface. Hot-dipping parameters and the detailed information about interface microstructure is exhibited in Table 5, Table 6, respectively.

Table 4.

The compositions (at.%) detected by EDS at red-color 1–9 site in Fig. 2.

site  Al  Fe  Si  Mn  site  Al  Fe  Si  Mn 
69.51  28.31  1.41  0.77  65.7  24.25  9.33  0.72 
70.13  23.54  6.20  0.13  70.73  13.38  14.43  1.01 
74.12  18.24  7.9  0.15  65.97  25.13  8.28  0.62 
68.7  24.68  6.5  0.12  73.73  10.23  16.01  0.03 
71.73  11.81  16.43  0.03           
Fig. 2.

Images (a), (b), (c) and (d) represent the morphology of Al/Fe bonding interface produced by hot-dipping Al–7.2wt.% Si melt, pure Zn melt, Zn–2.2wt.% Al melt and Zn–0.2wt.% Bi melt, respectively.

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Fig. 3.

XRD analysis on Al/Fe composite interface in Fig. 2(a)–(d).

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Table 5.

Hot-dip parameters of the hot-dipping Zn–Bi melt and the control groups of another three hot-dipping melts.

Hot-dipping melt  Hot-dipping temperature (K)  Hot-dipping time (s) 
Zn–0.2wt.% Bi melt  873±10  600±
Al–7.2wt.% Si melt  953±10  600±
Pure zinc melt  873±10  600±
Zn–2.2wt.% melt  873±10  600±
Table 6.

The detailed information on the microstructure of Al/Fe bonding interface in Fig. 2.

Image  (a)  (b)  (c)  (d) 
Hot-dipping melt  Al–7.2wt.% Si melt  Pure zinc melt  Zn–2.2wt.% Al melt  Zn–0.2wt.% Bi melt 
The phase constitution in the bonding interface  Al5Fe2, Al3Fe, Al8Fe2Si  Al5Fe2, Al5FeSi  Al5Fe2, Al5FeSi  Al5Fe2, Al5FeSi 
Width of intermetallic reaction layer  45–50μm  15–17μm  17–20μm  9–14μm 

Fig. 2(a) presents the thickest Al/Fe reaction layer with the dominant phase-the bigger, coarser polyhedral Al8Fe2Si (Table 6). It is well known that the thicker Al-rich phase layer readily leads to the fast fracture of Al/Fe bonding interface [13]. Therefore, the above features of interface microstructure should be responsible for the lowest shear strength of about 11MPa in Fig. 4. Fig. 2(b) describes the Al/Fe bonding interface with the same hot-dipping time and temperature as the shown in Fig. 2(c). It can be seen that the width and the phase constitution of Al/Fe reaction layer in Fig. 2(b) are nearly identical to that in Fig. 2(c). However, Fig. 2(b) presents more brittle-hard needle-like phases in Al matrix around Al/Fe interface, which is the main factor rendering shear strength (approximating 18MPa) lower than 20.0MPa of Al/Fe bonding interface in Fig. 2(c).

Fig. 4.

The shear strength of Al/Fe bonding interface induced by hot-dipping different melt: Al–7.2wt.% Si, pure Zn melt, Zn–2.2wt.% Al melt, and Zn–0.2wt.% Bi melt.

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Compared to Fig. 2(c), Fig. 2(d) shows a major difference that refers to the peculiar serrated morphology of Fe matrix. The serrated morphology differs obviously from the relatively flat Fe matrix in Fig. 2(c). The brittle-hard Al5FeSi phase, acting as the exacerbation of the fracture behavior, almost does not prevent the highest shear strength being possessed by the Al/Fe bonding interface in Fig. 2(d). All of these phenomena indicate that the formation of the concave–convex interface (CCI) is beneficial to increasing the shear strength of Al/Fe bonding interface.

3.2Effects of hot-dipping parameters in Zn–0.2wt.% Bi melt on the interface microstructure of Al/Fe bimetallic composites

Fig. 5 shows the cross-section of Al/Fe bimetallic composites with the hot-dipping time 480s at 873K. Region (A) and (B) surrounded by yellow dotted line are detected as Zn-rich regions by EDS and EMPA. The EDS detection on sites marked by 1, 2, 3, 4 presents that Zn content firstly decreases and then increases, indicating the segregation of Zn element at the region (A). The red dotted line-surrounded region (C) at the graphite–ferrite interface is Al–Fe phases in Fig. 5(a). The black-color zone in the region (A) in Fig. 5(a) is amplified in Fig. 5(b). The black-color zone is the cataclastic zone of ferrite corroded by elemental zinc, rather than the graphite because its coarse, semi-circle ends are distinguished from the blade-like ends of the graphite. In Fig. 5(c), region (D), (E), (F) that are detected as Zn-rich regions by EDS demonstrates that Zn-rich regions cause a degradation to the ferrite in cast iron.

Fig. 5.

(a) and (c) describe the cross-section of Al/Fe bimetallic composites with the dipping time of 480s at 873K. (b) represents the magnification image of the black-color zone in region (A) surrounded by yellow dotted line in image (a). (d) The zinc content detected by EDS on these sites marked by 1, 2, 3, 4 along the blue line in image (a).

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Considering distinctive materials and their corresponding manufacturing process, it is well-known that metallurgical and micromechanical aspect are controlled by the resulting microstructure, unsoundness, strength and ductility [33]. Based on this fact, the microstructure parameters are of high order to determine the resulting properties of materials (e.g. mechanical and corrosion responses of a number of distinctive alloys and materials [34–36]. Therefore, the microstructure array induced by hot-dipping parameters in present work is necessary to be exploited.

Fig. 6 exhibits six different interface morphologies from Al/Fe bimetallic composites with various shear strengths. The six interfacial morphologies display the different depth value of Al–Fe phases inserted in the graphite–ferrite interface of cast irons – 50μm, 34μm, 22μm, 18μm, 15μm, and 12μm. The shear strength from image (a)–(f) corresponds to 9±2MPa, 14±3MPa, 18±2MPa, 22±3MPa, 26±2MPa, 29±3MPa, respectively. Thus, the shear strength increases gradually with decreasing depth value of Al–Fe phases inserted in the graphite–ferrite interface. The width of Al/Fe reaction layer in image (a)–(f) almost stays within the range of 9–14μm. Changing hot-dipping parameters does not generate an obvious effect on the width of Al/Fe reaction layer. Image (a) illustrates the typical interface morphology with a low shear strength (8MPa) – Zn-rich regions in the ferrite, the bare graphite in the Al matrix as well as the largest inserting depth of Al–Fe phases in the graphite–ferrite interface. The intermetallic phase in the Al/Fe reaction layer in image (a)–(d) consists of Al5FeSi phase. Image (f) exhibits the typical interface morphology with a high shear strength (about 29±3MPa) – the smallest inserting depth, the serrated cast iron matrix with a relatively even Al/Fe reaction layer. From image (a)–(d), zinc content is found to appear in the Al–Fe phase inserted in the graphite–ferrite interface and decrease gradually along the Al–Fe phase toward the iron matrix. There may be a relationship between the Zn element and the formation of Al–Fe phases at the graphite–ferrite interface. The phenomenon that the increased inserting depth of Al–Fe phases in the graphite–ferrite interface can decrease the maximum shear stress necessary to damage Al/Fe bonding interface can be also understood by the fracture behavior of Al/Fe bonding interface.

Fig. 6.

SEM images of cross-section of Al/Fe bimetallic composites with various shear strength. The shear strength induced by different interfacial morphology in SEM image (a)–(f) corresponds to 9±2MPa, 14±3MPa, 18±2MPa, 22±3MPa, 26±2MPa, 29±3MPa, respectively.

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From Fig. 7(b) and (c), it can be seen that cracks always occur at the position in which Al–Fe phases appear. Although cracks also occur at the Al/Fe interfacial reaction layer when Al–Fe phases form in the ferrite–graphite interface, the damage induced by shear stress is mainly concentrated in the graphite–ferrite interface – is to separate parts of ferrite from the cast iron (Fig. 7(b)). Thus, the formation of Al–Fe phases at the graphite–ferrite interface can weaken the bonding performance between the ferrite and the cast iron matrix. The greater inserting depth of Al–Fe phases in the graphite–ferrite interface can generate a stronger weakening effect on Al/Fe bonding performance, resulting in a decreased maximum shear stress necessary to damage the Al/Fe bonding interface.

Fig. 7.

(a) The relation of shear strength with the inserting depth of Al–Fe phases at the graphite–ferrite interface. (b) The fracture occurs at the graphite–ferrite interface and Al/Fe interfacial reaction layer when Al/Fe phases form at the graphite–ferrite interface. (c) The fracture occurs at the Al/Fe interfacial reaction zone when no Al/Fe phases form at the graphite–ferrite interface.

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We also exploited the percentage of the fiber-like graphite distribution in Fig. 6 by using the software ‘IMAGE J’. Fig. 8(a)–(f) presents the analysis images of the percent of fiber-like graphite and correspond successively to the Fe matrix shown in Fig. 6(a)–(f), respectively. The percent of fiber-like graphite from Fig. 8(a)–(f) is about 10.21%, 9.16%, 6.53%, 5.36%, 5.69%, 5.5%. Although the increasing of shear property is seemingly accompanied with the decreasing of the percent of fiber-like graphite in Fe matrix around the Al/Fe interface, there is actually not the relation between the percent of graphite in Fe matrix and the shear property because the fracture exists only in a very narrow area with the center of Al/Fe interface.

Fig. 8.

Analysis image of the percent of graphite closed to the Al/Fe composite interface. Image (a)–(f) corresponds to the (a)–(f) in Fig. 6.

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4Discussion4.1Effects of Bi element on the interface morphology of Al/Fe bimetallic composites

From Fig. 9(a) and (b), we can find that no Al–Fe phases appear in the graphite–ferrite interface under the condition of hot-dipping in pure Zn melt. In Fig. 9(c) and (d), there are Al–Fe phases found to form in the graphite–ferrite interface around the Al/Fe bonding interface induced by hot-dipping in Zn–Bi melt. Several white-color stripes marked by red-color arrows in Fig. 9(d) are detected by EMPA as Zn-rich regions which appear at the internal of Al–Fe phases. From the relative positions of both them, it can be seen that the emergence of Zn-rich regions in the cast iron matrix is earlier than Al–Fe phases. In particular, Al–Fe phases at the graphite–ferrite interface is always accompanied with zinc element (Fig. 6), suggesting that Al–Fe phases form at the graphite–ferrite interface with a premise of the presence of Zn element. The guess may be understood by the following process. Since Zn-rich regions have a dilatation coefficient differing from cast iron matrix, spatial sparseness is created due to the difference in the thermal strain between Zn-rich regions and cast iron matrix under the high temperature, and then the Al element diffuses rapidly into the vacant sparser regions toward the cast iron matrix by creating the resultant ternary phases – Al–Fe phases with a small amount of Zn element.

Fig. 9.

The SEM image of cross-section of Al/Fe bimetallic composites induced by hot-dipping pure Zn melt and Zn–Bi melt, respectively, with the same hot-dipping time 600s, temperature 833K and pouring temperature of 993±10K. Images (a) and (b) correspond to hot-dipping pure Zn melt method. Images (c) and (d) correspond to hot-dipping Zn–Bi melt method.

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Only under the condition of hot-dipping in Zn–Bi melt do Zn-rich regions appear at the surface layer of cast iron. The addition of Bi element into Zn melt plays a positive role in the formation of Zn-rich regions at the surface layer of cast iron, because adding a trace of Bi element into zinc melt enhances the liquidity of zinc melt [37], and thus enhances the Zn melt’ erosion-corrosion effect on cast iron. The enhanced penetration of zinc element toward the cast iron matrix causes the zinc accumulation at the surface layer of cast iron.

4.2Formation process of concave–convex interface caused by the serrated cast iron matrix during Al/Fe composite process

The formation of CCI is closely related to the formation of Al–Fe phases at the graphite–ferrite interface. Firstly, Zn–Bi coatings fuse into the hyperthermia aluminum alloy melt in Fig. 10(a). A thin Al–Fe phases layer form primarily on the cast iron with an Al/Fe metallurgical reaction in Fig. 10(b). Gradually, Al–Fe phases grow along the graphite–ferrite interface corroded by Zn-rich regions toward the cast iron matrix in Fig. 10(c). At this time, two types of graphite morphology avail to form the CCI, which are the I graphite morphology called by us that has both ends connected to Al/Fe interface reaction layer in Fig. 10(g) and the II graphite morphology that is a graphite group having two graphite intersected with each other in Fig. 10(h). With Al–Fe phases going gradually deep into the graphite–ferrite interface, the bonding interface of graphite (I and II graphite)/ferrite is substituted with a new bonding interface between Al–Fe phases and graphite in Fig. 10(d). Affected by a temperature fluctuation in the high temperature aluminum alloy melt, the new bonding interface is readily destroyed owing to Al–Fe phases re-melts, and parts of ferrite surrounded already by Al–Fe phases is forced to migrate and separate gradually from cast iron matrix (Fig. 10(e) and (f)). Fig. 10(g) and (h) displays the actual processes that the ferrite surrounded already by Al–Fe phases fails to be separated completely from cast iron matrix owing to cooling Al/Fe composite system too fast. After the ferrite is separated completely from the cast iron matrix, aluminum alloy melt flows into those positions lacking of ferrite, consequently resulting in a specular structure of the serrated cast iron attached with a relative even Al–Fe phase layer, called the concave–convex interface (CCI).

Fig. 10.

Images (a)–(f) illustrate a model about the formation process of concave–convex interface induced by changing iron matrix. Images (g)–(i) depict the actual process of changing iron matrix during Al/Fe composite process.

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4.3Analysis of stress state in concave–convex interface region to enhance the shear strength of Al/Fe bimetallic composites

Al/Fe composite specimens prepared by dipping Zn–0.2wt.% Bi melt is subjected to a pair of shear forces near the interface in the experiment. The fracture surface of the specimens is nearly a plane parallel to the direction of the shear force . Thus, the state of stress on the interface of the specimen under the action of shear forces is nearly in pure state of shear and the state of plane stress. The state of stress acting on the small element of the interface is shown in Fig. 11(a). Only the shear stresses exist on faces of the small element, which are parallel and perpendicular to the x-axis, respectively (Fig. 11(a)). Based on the analysis of stress state, the stress acting on the element oriented at an angle α from the x-axis can be determined by the following equation [38].

Fig. 11.

(a) The stress state acting on faces of small element of the interface. (b) Mohr's circle related to (a), σ-axis represents the direction of maximum tensile stress, and τ-axis represents direction of maximum shear stress.

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The stress condition in any direction shown in Fig. 11(a) can be represented by the Mohr's circle in Fig. 11(b). It can be seen from Eqs. (1) and (2) and Mohr's circle that shear stress on the small element in the Fig. 11(a) is its maximum shear stress, which is represented by the state of stress at the point B in Fig. 11(b). The maximum tensile stress located on the element rotated through −45° about x-axis and is represented by the point A in Fig. 11(b), is the same as the maximum shear stress. It can be therefore shown that the crack along the interface is only due to the shear stress, and not due to the tensile stress. From the Mohr's circle, it can be seen that the shear stress on the plane rotated through an angle α (α 0), such as the point C, is always less than the shear stress on the plane perpendicular to the x-axis, i.e. on the interface. If the interface is rotated through an angle α with respect to the x-axis, the shear stress on the interface is always less than the applied shear stress, so that the shear strength of the joint is, to a decisive extent, increased since the shear strength of the base material is much stronger than the shear strength of the interface. Therefore, the joint whose interface is designed as concave–convex shape will have much greater shear strength than the normal joint having the straight interface parallel to the shear force.

The experiment confirms that Al/Fe bimetallic composites with CCI produce composites with super-high shear strength, and this is a solid advancement in the field of bimetallic composite casting.

5Conclusions

In present work, a new composite technology consisting of the surface pretreatment on cast iron matrix, the hot-dipping in Zn–Bi (Zn–0.2wt.% Bi) melt and the Al/Fe composite process, is developed to obtain an Al/Fe (aluminum alloy/casting iron) bimetallic composite with a super-high shear strength of 32MPa. The shear strength of Al/Fe bimetallic composites induced by hot-dipping in Al–7.2wt.% Si melt, pure Zn, Zn–2.2wt.% Al melt, can be approximately up to 11MPa, 19MPa, 22MPa, respectively. The increase of shear strength is mainly attributed to the formation of concave–convex interface (CCI) structures caused by the serrated cast iron matrix. This kind of CCI differs from the irregular Al reaction layer with dominant phases – big, blocky Al8Fe2Si induced by hot-dipping in Al–Si (Al–7.2wt.% Si) melt. The addition of Bi element into the zinc melt promotes the formation of Zn-rich regions in the graphite–ferrite interface and surface layer of parts of ferrite, consequently leading to the formation of Al–Fe phases at the graphite–ferrite interface. With Al–Fe phases at the ferrite–graphite interface propagating toward the cast iron matrix, a new bonding interface between graphite and Al–Fe phases is established, weakening the bonding performance between ferrite and the cast iron matrix.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 51371107 and 51571130). The authors are grateful for the help from the teacher: Erping Wang, School of Materials Science and Engineering, Beijing Industry University, Beijing 100022, China.

References
[1]
S. Basak, H. Das, T.K. Pal.
Characterization of intermetallics in aluminum to zinc coated interstitial free steel joining by pulsed MIG brazing for automotive application.
Mater Charact, 112 (2016), pp. 229-237
[2]
F. Bonollo, I. Carturan, G. Cupitò, R. Molina.
Life cycle assessment in the automotive industry: comparison between aluminium and cast iron cylinder blocks.
Metall Sci Technol, 24 (2013),
[3]
A. Lombardi, F. D’Elia, C. Ravindran, R. MacKay.
Replication of engine block cylinder bridge microstructure and mechanical properties with lab scale 319 Al alloy billet castings.
Mater Charact, 87 (2014), pp. 125-137
[4]
Y.C. Lim, L. Squires, T. Pan, M. Miles, G. Song, Y.L. Wang, et al.
Study of mechanical joint strength of aluminum alloy 7075-T6 and dual phase steel 980 welded by friction bit joining and weld-bonding under corrosion medium.
Mater Des, 69 (2015), pp. 37-43
[5]
U. Dilthey, L. Stein.
Multimaterial car body design: challenge for welding and joining.
Sci Technol Weld Joi, 11 (2013), pp. 135-142
[6]
G. Meschut, V. Janzen, T. Olfermann.
Innovative and highly productive joining technologies for multi-material lightweight car body structures.
J Mater Eng Perform, 23 (2014), pp. 1515-1523
[7]
F. Haddadi, D. Strong, P.B. Prangnell.
Effect of zinc coatings on joint properties and interfacial reactions in aluminum to steel ultrasonic spot welding.
JOM, 64 (2012), pp. 407-413
[8]
G. Barbezat.
Advanced thermal spray technology and coating for lightweight engine blocks for the automotive industry.
Surf Coat Technol, 200 (2005), pp. 1990-1993
[9]
W. Jiang, Z. Fan, G. Li, X. Liu, F. Liu.
Effect of hot-dipping galvanizing and aluminizing on the interfacial microstructure and mechanical properties of aluminium alloys/iron bimetallic composites.
J Alloys Compd, 688 (2016), pp. 742-751
[10]
P. Obert, T. Müller, H.-J. Füßer, D. Bartel.
The influence of oil supply and cylinder liner temperature on friction, wear and scuffing behavior of piston ring cylinder liner contacts – a new model test.
Tribol Int, 94 (2016), pp. 306-314
[11]
K.J.M. Papis, B. Hallstedt, J.F. Löffler, P.J. Uggowitzer.
Interface formation in aluminium–aluminium compound casting.
Acta Mater, 56 (2008), pp. 3036-3043
[12]
Y. Liu, X.F. Bian, K. Zhang, L. Feng, H.S. Kim, J. Guo.
Interfacial microstructures and properties of aluminum alloys/galvanized low-carbon steel under high-pressure torsion.
Mater Des, 64 (2014), pp. 287-293
[13]
T. Ogura, T. Nishida, Y. Tanaka, H. Nishida, S. Yoshikawa, M. Fujimoto, et al.
Microscale evaluation of mechanical properties of friction stir welded A6061 aluminium alloy/304 stainless steel dissimilar lap joint.
Sci Techol Weld Joi, 18 (2013), pp. 108-113
[14]
W.H. Zhang, D.Q. Sun, L.J. Han, D.Y. Liu.
Interfacial microstructure and mechanical property of resistance spot welded joint of high strength steel and aluminium alloy with 4047 AlSi12 interlayer.
Mater Des, 57 (2014), pp. 186-194
[15]
T. Ogura, Y. Saito, T. Nishida, H. Nishida, T. Yoshida, N. Omichi, et al.
Partitioning evaluation of mechanical properties and the interfacial microstructure in a friction stir welded aluminum alloy/stainless steel lap joint.
Scripta Mater, 66 (2012), pp. 531-534
[16]
H. Bang, H. Bang, G. Jeon, I. Oh, C. Ro.
Gas tungsten arc welding assisted hybrid friction stir welding of dissimilar materials Al6061-T6 aluminum alloy and STS304 stainless steel.
Mater Des, 37 (2012), pp. 48-55
[17]
A. Heidarzadeh, H. Khodaverdizadeh, A. Mahmoudi, E. Nazari.
Tensile behavior of friction stir welded AA 6061-T4 aluminum alloy joints.
Mater Des, 37 (2012), pp. 166-173
[18]
J. Ma, M. Harooni, B. Carlson, R. Kovacevic.
Dissimilar joining of galvanized high-strength steel to aluminum alloy in a zero-gap lap joint configuration by two-pass laser welding.
Mater Des, 58 (2014), pp. 390-401
[19]
T.A. Mai, A.C. Spowage.
Characterisation of dissimilar joints in laser welding of steel–kovar, copper–steel and copper–aluminium.
Mater Sci Eng A, 374 (2004), pp. 224-233
[20]
G. Sierra, P. Peyre, F. Deschaux-Beaume, D. Stuart, G. Fras.
Steel to aluminium key-hole laser welding.
Mater Sci Eng A, 447 (2007), pp. 197-208
[21]
H.T. Zhang, J.C. Feng, P. He, B.B. Zhang, J.M. Chen, L. Wang.
The arc characteristics and metal transfer behaviour of cold metal transfer and its use in joining aluminium to zinc-coated steel.
Mater Sci Eng A, 499 (2009), pp. 111-113
[22]
J. Feng, H. Zhang, P. He.
The CMT short-circuiting metal transfer process and its use in thin aluminium sheets welding.
Mater Des, 30 (2009), pp. 1850-1852
[23]
A.R. Riahi, O.A. Gali, K.R. Januszkiewicz, D. Pattemore.
Experimental study of the disturbed layer generation during hot rolling contact of aluminum with steel.
Tribol Int, 54 (2012), pp. 42-50
[24]
T. Ma.
(2013), pp. 5-8
[25]
Y. Abe, K. Mori, T. Kato.
Joining of high strength steel and aluminium alloy sheets by mechanical clinching with dies for control of metal flow.
J Mater Process Technol, 212 (2012), pp. 884-889
[26]
R.K. Tayal, V. Singh, S. Kumar, R. Garg.
Compound casting – a literature review.
Proceeding of national conference on trends and advances in mechanical engineering,
[27]
Y. Liu, X.F. Bian, J. Yang, K. Zhang, L. Feng, C.C. Yang.
An investigation of metallurgical bonding in Al–7Si/gray iron bimetal composites.
J Mater Res, 28 (2013), pp. 3190-3198
[28]
W. Jiang, Z. Fan, C. Li.
Improved steel/aluminum bonding in bimetallic castings by a compound casting process.
J Mater Process Technol, 226 (2015), pp. 25-31
[29]
A. Malakizadi, I. Sadik, L. Nyborg.
Wear mechanism of CBN inserts during machining of bimetal aluminum-grey cast iron engine block.
Procedia CIRP, 8 (2013), pp. 188-193
[30]
O. Dezellus, B. Digonnet, M. Sacerdote-Peronnet, F. Bosselet, D. Rouby, J.C. Viala.
Mechanical testing of steel/aluminium–silicon interfaces by pushout.
Int J Adhes Adhes, 27 (2002), pp. 417-421
[31]
L. Sun, C.A. Li, J.W. TU, M.C. Peng.
Effect of surface treatment to inserted ring on Al–Fe bonding layer of aluminium piston with reinforced cast iron ring.
J Cent South Univ, 21 (2014), pp. 3037-3042
[32]
S. Shibli, B. Meena, R. Remya.
A review on recent approaches in the field of hot dip zinc galvanizing process.
Surf Coat Technol, 262 (2015), pp. 210-215
[33]
N.J. Petch.
The cleavage strength of polycrystals.
J Iron Steel Inst, 174 (1953), pp. 25-31
[34]
W.R. Osorio, L.C. Peixoto, M.V. Canté, A. Garcia.
Electrochemical corrosion characterization of Al–Ni alloys in a dilute sodium chloride solution.
Electrochim Acta, 55 (2010), pp. 4078-4085
[35]
P. Donelan.
Modelling microstructural and mechanical properties of ferritic ductile cast iron.
Mater Sci Technol, 16 (2000), pp. 261-269
[36]
W.R. Osório, P.R. Goulart, G.A. Santos, C. Moura Neto, A. Garcia.
Effect of dendritic arm spacing on mechanical properties and corrosion resistance of Al 9 wt% Si and Zn 27 wt% Al alloys.
Metall Mater Trans A, 37 (2006), pp. 2525-2538
[37]
N. Pistofidis, G. Vourlias, S. Konidaris, E. Pavlidou, A. Stergiou, G. Stergioudis.
The effect of bismuth on the structure of zinc hot-dip galvanized coatings.
Mater Lett, 61 (2007), pp. 994-997
[38]
S.P. Timoshenko, J.N. Goodier.
Analysis of stress and strain.
(2000), pp. 498
Journal of Materials Research and Technology

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