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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.2019.01.029
Open Access
Inspection of casting defects and grain boundary strengthening on stressed Al6061 specimen by NDT method and SEM micrographs
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A. Bovas Herbert Bejaxhina,
Corresponding author
herbert.mech2007@gmail.com

Corresponding author.
, G. Paulrajb, M. Prabhakarc
a Department of Mechanical Engineering, SRM TRP Engineering College, Irungalur, Trichy, Tamil Nadu 621105, India
b Department of Mechanical Engineering, VEL TECH, Avadi owned by R.S. Trust, Avadi, Chennai, Tamil Nadu 600062, India
c SRM TRP Engineering College, Irungalur, Trichy, Tamil Nadu 621105, India
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Tables (5)
Table 1. Composition of Al6061 alloy.
Table 2. Displacement values of various hot forming casting specimen.
Table 3. Brinell and Rockwell hardness of casting samples after hot pressing.
Table 4. Nondestructive testing report of Al6061 casting samples.
Table 5. SEM Micro structure remarks of particle size and grain boundary thickness (μm).
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Abstract

Non-destructive testing is one part of the function of quality control and is complementary to other long-established methods. By definition, non-destructive testing is the testing of materials, for surface or internal flaws or metallurgical condition, without interfering in any way with the integrity of the material or its suitability for service. The methods covered are Radiography, Magnetic Particle Crack Detection, Dye Penetrate Testing, Ultrasonic Flaw Detection, Eddy Current and Electro-Magnetic Testing. Here in this project work by using the radiography method of NDT testing is followed to identify the internal defects of the Al6061 cast specimen that was made by stir casting method. The aluminum cast structure involved to mono and multi-heat treated at about 450°C and 600°C in a muffle furnace and is compressed mechanically by using hydraulic press arrangements before the brief inspection through NDT testing. This technique is suitable for the detection of internal defects in ferrous and nonferrous metals and other materials. Furthermore, the denser the material greater will be the absorption. After the primary stage of inspection, most of the defects were identified by the NDT methods. In the second part of this project, SEM images can be taken for the compressed casting structure. The structural changes were successfully made on the cast specimen and the bond strength, as well as hardness were also increased. The comparison was made between the NDT inspected values and the SEM microstructure. It shows the clear representation of the grain structure and the bond strength.

Keywords:
Casting
Nondestructive testing
Hardness
SEM
Hot forming
Nomenclature
t

specimen thickness (mm)

W

compressive load (kN)

N

rotational speed (rpm)

BHN

Brinell hardness number

HT

heat treatment

FT

forming temperature (°C)

SEM

scanning electron microscope

NDT

non-destructive testing

Full Text
1Introduction

Casting process is one of the earliest metal shaping techniques known to human being. It means pouring molten metal into a refractory mold cavity and allows it to solidify. The solidified object is taken out from the mold either by breaking or taking the mold apart. While casting there will be a lot of defects. It is essential to identify all those defects and minimize them to almost defect free cast components. In aluminum castings, structural defects, oxide bi-films (folded oxide films entrained into the melt during the casting of the metal) and pores are common as a result of poor melt quality and/or mold filling system design. These structural defects have deleterious effects on the tensile strength and elongation as well as the fatigue life. Testing and evaluation of cast products in a foundry industry has one primary objective. It is to make sure that parts being produced actually meet all required specifications established by the customer. Use of non-destructive testing and evaluation (NDT&E) as a means of quality control permits the industries to produce better quality products [1]. Nondestructive testing is extensively functional in many plants, aerospace, nuclear industry, military and defence, storage tank inspection, pipe and tube inspection and composite defects characterization. Dwivedi et al. discussed in this paper mainly focuses on the scope of NDT application for composite materials [2]. To ensure the quality of the parts produced by introducing WAAM to evaluate the potential of the existing NDT testing was focused by Lopez et al., they found that for in-process inspection Eddy Current (EC), ultrasonic (UT) and thermography are the most suitable methods while EMAT or Laser UT have less limitation and can be a good approach. Better methods which are suitable for various defect identification methods and its suitability was explained [3]. The testing time is absolutely reduced by using EMAT is a proper tool for fatigue characterization for inspecting the crack initiation through online mode verified by Dobmann [4]. Adopting the reliable method for NDT testing of boiler tubes inspection by Vakhguelt et al., it was concluded that the combination of wall thinning or overheating was the major damage mechanism. Two ultrasonic test measures were suggested for early detection of both these damage types without removing tube from the boiler. Ferritic-pearlitic structure observed in all samples with occasional inclusions in ferrite grains. The creep indication was identified from the metallurgical structures due to some elongated grains and structural degradation by Vakhguelt et al. [5]. The reinforced Si particulate effect on aluminum alloy highlighted the enormous potential strength was verified by Mueller et al. The weakening effects of defects found in the Al-Si and Al-Si-Mg alloys from the SEM and micromechanical testing methods [6]. The grain sizes in the microstructural outcomes on various places of billet as well as the increased levels of ultimate tensile strength and yield strength were highlighted by Zheng et al. [7]. High strain was developed around the sharp edge of the insert when the high temperature and load is acting. The transition between recrystallized and martensitic showed the deformation levels from the SEM investigation by Marashi et al. [8]. Nakasato et al., discussed that the yield stress of the material is lowered by elevating the temperature, and the material tends to be locally deformed without work hardening. In higher temperature spinning, it is considered that the large compressive plastic deformation occurs at the spinning temperature of 4000°C [9]. Formability of aluminum alloy thin-walled cylinder parts by servo hot stamping process was discussed by Song et al., the maximum plastic strain at dangerous point is much lower in the thin walled cylinder parts resulting in the formability improvement of AA7075 sheets [10]. By laser melting most commonly used titanium alloy Ti–6Al–4V specimens produced and showed that the microstructure and strain hardening of specimens produced by SLM and it can be refined during hot working and distributed well along the phases [11]. Here the finite element model has been created and validated from experimental results. The evaluation of the formability and failure of materials in hot stamping processes were discussed by Lin et al., the FE model used to achieve an accurate failure prediction. It is verified that the size of the hole is also related to the ductility of the material surely related to temperature and strain rate [12]. The influence of different parameters on the fracture surface quality during the process of hot stamping were analyzed and verified by Lei et al., for the blanking process simulation for hot stamped parts forming under 750°C are better than others and the clearance of 10% sheet thickness is a good choice for hot blanking die, less wear and tear [13]. The simulated temperature evolutions obtained using the FE software PAM-STAMP to determine the corresponding interfacial heat transfer coefficient (IHTC) values by Wang et al., The required contact pressure and temperature The peak IHTC value decreased to 10kW/m2K when using Tool 2, and was due to the less thermal conductivity of Tool 2 [14]. It was found by Xu et al., that the predicted defects in the titanium alloy casing matched well with the actual X-ray experimental results. It showed that the gravity casting process can be more reasonable than the centrifugal casting process which has no obvious improvements in the concentrated shrinkage defects [15]. The low cost stir casting processing of magnesium alloy and its composite with flux and without flux was explained by Kumar et al., the ultimate tensile strength and ductility were improved by the addition of reinforced particles with the Mg-Al alloys. Fintová et al. [16] studied the cast AlSi7Mg alloy prepared using different modifier and found that the main factor influencing fatigue properties were the casting defects. Using metallography and statistical approach, Larger Extreme Value Distribution (LEVD) theory, the structure and the porosity were evaluated. Fatigue cracks were initiated on the casting defects present on the specimen free surface or just below the surface identified using SEM. Specimens fatigue life was influenced by the size of the defect in the initiation place and the number of initiation places.

Here in this research work, for the purpose of identify the internal failures like cracks, blowholes, voids and air bubbles in a very easy manner on the casting specimens, comparison of the structural bond strength between the ordinary specimen and the compressed one by following with hot pressing principles. The regulation of a hardness to a certain level best by hot pressing and different heat treatments like mono heat treatment and multi heat treatments was done on the specimen samples and finally it is easy to differentiate the micro constitutions of NDT tested aluminum samples for the identification of particle size and grain boundary in a very absolute pixel by SEM micrographs.

2Experimental2.1Material selection and specimen preparation

In the initial stage the material was purchased based on literature survey and experimental plan. Initially the aluminum alloy was chosen because of light in weight high strength material with more ductile and optimum hardness. The availability of the materials is more and also the cost becomes low compare with other nonferrous materials. So we selected Al6061 alloy material which is most extensively used of the 6000 series aluminum alloys. It is a versatile heat treatable extruded alloy with medium to high strength capabilities.

Stir casting is an inexpensive method of melting and fabricating the required metal matrix composites in which a disseminated segment is mixed with the reinforcement additives for the recommended shapes and sizes. The mixing or stirring of molten metal and the addition of reinforcements with the electric motor coupled with the stirrer placed vertically above the furnace arrangements. The molten slag was mixed with the reinforcements and its additives by mechanical stirring action by graphite stirrer rod. It is completely cost effective and qualitative too. It contains magnesium and silicon as major alloying elements which is shown in Table 1, also having density of 2700kg/cm3 which is exactly suitable for high strength low weight applications. The required shapes of the specimen are created by the stir casting process. The casting was done in the high temperature molding furnace which is having the melting temperature range of 900–1200°C, very suitable for making non-ferrous castings. The casting specimen shape was turned back in the form of rectangular blocks each of certain size 50mm×50mm×40mm as shown in Fig. 1.

Table 1.

Composition of Al6061 alloy.

Component  Al  Mg  Si  Fe  Cu  Zn  Ti  Mn  Cr  Others 
Weight (%)  Balance  0.8–1.2  0.4–0.8  Max 0.7  0.15–0.40  Max 0.25  Max 0.15  Max 0.15  0.04–0.35  0.05 
Fig. 1.

Preparation of specimen by stir casting of Al 6061.

(0.09MB).
2.2Innovative heat treatment of casted specimen

After completing the casting process through machining these specimens were prepared and it is involved to primary mono heat treatment at a temperature of 450°C for certain time with annealed and quenched mode. After that the 600°C in multi heat treatment processes was obtained over the specimens which were annealed and quenched earlier with mono heat treatment. Totally four specimens out of eight were heat treated by mono heat treatment at a temperature of 600°C with annealed and quenched manner. In multi heat treated methods, the remaining four specimens were treated first with 450°C then after the completion of hardening by anneal or quenching those are coming in to the secondary heat treatment with the temperature of 650°C. The same air hardening and quenching has followed after completion of the multi heat treatment process. The heat treatment was done by using the muffle furnace KSM-0012 shown in Fig. 2 which has usable chamber size of 100mm×100mm×225mm with the operating temperature of 1000°C maximum up to 1200°C.

Fig. 2.

Heat treatment of Al6061 cast specimen with the mono and multi heat treatment methods.

(0.12MB).

The specimens were well hardened and treated by using the annealing and quenching stages at all levels of forming temperatures. The secondary heat treated specimens were treated with the temperature of 600°C. It will motivate the process by which distorted grains of cold or hot forming metal were replaced by the new strain free grains during this additional heat treatment. It becomes the material more ductile, hardness and refined grain structure.

2.3Measurement of hardness and NDT testing on hot pressed specimen

After the completion of heat treatments, the specimens were suddenly involved for the hot pressing by using the Universal Testing machine FIE-Universal 2001 (UTE). The specimens were involved in this hot pressing by UTM with the gradually applied compressive load of 400kN before quenching and annealing as shown in Fig. 3. The displacement and load values are noticed from the electronic display in the output response panel of UTM. After that the specimens were suggested for hardness measurement as shown in Fig. 4. Defect less casting specimen were prepared successfully by the casting of pure Al6061 alloy material and the heat treatment highly removed all the internal stresses and defects of the specimen.

Fig. 3.

Hot pressing of Al6061 heat treated cast specimen in UTM machine.

(0.09MB).
Fig. 4.

Hardness testing and its impression on heat treated hot pressed Al6061 casted specimen.

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Better hardness were identified the ability of resisting the loads among various samples which is clearly agreed that more hardness is chanced in multi heat treated samples compared with the mono heat treated samples. By using Brinell and Rockwell hardness tester, the BHN and RHN values of each hardened specimens were measured by using steel ball intender with the load of 2000kgF. By measuring the impression of indentation to identify the values of BHN in an easy manner.

The defects were also identified by the radiography method of NDT which is clearly assured that the no defects level of outputs after the specimen met these kind of heat treatments. The scanning electron microscope (SEM) readings were collected for the highlighted casted piece for finding the grain strength and particle size in a micro level of observations. Finally, the SEM readings of the sample specimens and NDT results of the same were analyzed and the readings were tabulated.

2.4Dynamic analysis of hot forming in Deform 3D

There are three stages preprocessing, solution and post processing stages of analysis were performed in Deform 3D as mentioned in Fig. 6. The finite element model and the sketch of thick rectangular AL6061 casted specimen drawing are shown in Fig. 5. The FE model consists of three parts, namely the top and bottom die, in between the specimen model were located with the auto positioning through coordinate systems. Using various iterations of hot forming by using the dynamic simulator Deform 3D. In this simulation the preliminary steps the input parameters of die temperature and object shape complexity has given. The compressing loads due to punching effect and boundary conditions were specified for the bottom die as fixed.

Fig. 6.

Deform 3D process tree.

(0.15MB).
Fig. 5.

Mesh generation of hot forming specimen with primary and secondary die arrangement in the dynamic simulator deform 3D.

(0.42MB).

The material properties are also mentioned as Al6061 from the material library which is automatically included all the data related to the material behavior. After the process steps got over the specimen model was developed by the dimensions given in the geometry primitive with the plastic deformation type. The Brick element type and the iteration levels has given. After the completion of boundary conditions, the movable and fixed jaws were indicated. The specimen shape with the dimensions of 50mm×50mm×40mm and the solid mesh generated with 18,630 elements and 4278 nodes as shown in Fig. 5. The punch always was fixed, the downward movement of the die controlled by a motion curve, while the outright frame applied an upward force with the value of 400kN. The initial forming temperature of the blank was 450–650°C and the initial temperatures of the die and the punch were 25°C. The surface interaction contact was used in the model. The die and specimen arranged by auto positioning with the friction coefficient of 0.7 and heat transfer coefficient of 5W/mK has been set for the dry hot forming condition. The stress and displacement values were identified as output responses after the completion of each iterative simulation for various load and forming temperatures given as input parameters as shown in Fig. 7.

Fig. 7.

Simulation results of displacements on castings for 450°C and 600°C (P=400kN).

(0.39MB).
3Results and discussion

During the hot forming process of Al 6061 alloy casting without any reinforcements the specimens were prepared by casting. Two heat treatment processes were followed after the hot pressing through the hydraulic press action in UTM machine. The specimen thickness was reduced from its initial shape because of moderate time interval of applied load of 400kN. The forming temperatures were maintained as 600°C and 450°C. The forming temperatures based on the acceptable levels of melting temperatures of aluminum alloys and its castings which is exactly nearby 650°C. There are two stages of hot pressing and heat treatments were initiated such as mono heat treatment and multi heat treatment for the constant pressing force of 400kN. In the primary stage of mono treatment, the casted specimen heated at the temperature of 600°C in the muffle furnace KSM-MF01 as shown in Fig. 2 which is having temperature range of maximum 1000°C. After reaching the annealing temperature of 600°C which is almost grasped as liquid solution the specimen immediately involved in hot pressing by using FIE Universal testing machine 2001 (UTE) as shown in Fig. 3. The hot specimen was pressed and then annealed for certain holding time for getting more hardness and good mechanical properties were attained. During the quenching process the hot specimen were dipped in to the water solution.

3.1Calculation of displacement variation

Here the displacements were calculated from its initial thickness of each specimen after hot pressed and it is mentioned in Table 2. The deformation levels were well predicted through the dynamic analysis software tool Deform 3D. These predicted graphical values of displacements are compared with the measured change in thickness values. We have to calculate the displacement as change in thickness of the hot presses specimen under various heat treatment processes. The predicted values are obtained from the modern tool usage. The calculated displacement of the hot pressed specimen is as follows in Eq. (1):

where ti is the initial thickness of the specimen after casting and tf is the final thickness of the specimen after hot pressing.

Table 2.

Displacement values of various hot forming casting specimen.

No.  FT (°C)  W (kN)  HT  t (mm)  x (mm)Variation 
          Predicted  Calculated   
600 (Mono HT)400Annealing34.61  5.26  5.39  0.13 
24.71  5.87  15.29  9.42 
Quenching38.22  4.26  1.78  2.48 
25.62  4.79  14.38  9.59 
450 & 600 (Multi HT)Annealing29.30  4.49  10.7  6.21 
37.00  3.94  0.94 
Quenching34.52  4.87  5.48  0.61 
31.31  4.96  8.69  3.73 
3.2Simulation results of hot forming

Using various iterations of hot forming by using the dynamic simulator Deform 3D. In this simulation the preliminary steps the input parameters of compressing loads and boundary conditions were added. The materials properties also mentioned as Al6061 alloy from the material library which is automatically included all the data related to the material behaviors. After the process steps got over the specimen model imported and the iteration levels are to be set. After the completion of boundary conditions, the movable and fixed jaws were indicated. Various loads and forming temperatures are also given as input parameters. The stress values and displacements were identified as output responses after completion of the iterative simulations. Here the less displacement was recorded as 3.94 for the annealed multi heat treated sample as shown in Fig. 7. Larger displacements were attained during the mono heat treated samples. The variation among all the experiments, these two heat treatments were showed clearly the least values of variation 0.61, 0.94 was attained during the multi heat treatment stage at a temperature of 650°C for the load of 400kN.

3.3Comparison of hardness in hot pressed specimens

It is confirmed that the predicted values of displacement in dynamic simulation tool Deform 3D in hot forming, the displacement variation is minimum during the multi heat treated specimen inspection because of change in thickness varying depends on the heating temperatures at about 600°C. The grain boundary thickness and particle size were recorded minimum due to the hot compressed multi heat treated Al6061 samples. The strain rate becomes high used to change the particle size minimum. Better observations of particle size reduction, grain boundary strengthening and high hardness were acknowledged good in multi heat treated hot pressing of Al6061 casting samples. There were no more defects were identified in NDT among the both mono and multi heat treated casting samples. After the heat treatment and hot forming is over, the hardness of each specimen were calculated and the observations are mentioned in Table 3 as shown above. Both Brinell (BHN) and Rockwell hardness (RHN) testing were done on the treated specimen in both levels of forming stages. Here we clearly identified the hardness of multi heat treated specimen has got wonderful hardness 111.81 BHN and 65.365 RHN, respectively. Compared with the mono heat treated specimen higher hardness were achieved in the variation of 2.5125 hardness number with the multi heat treated specimen. It is noted that the less hardness values were recorded in the non-heat treated specimen as 99.25 BHN and 58.77 RHN. Higher hardness was obtained on the quenching specimen in the multi heat treatable.

Table 3.

Brinell and Rockwell hardness of casting samples after hot pressing.

S. No.  Forming temp (°C)  Comp load (kN)  Heat treatment  Specimen thickness (mm)  Hardness
          BHN  Avg.  RHN  Avg. 
600 (mono heat treatment)400Annealing34.61  99.25  108.26 BHN58.77  62.8525 RHN
24.71  124.82  70.76 
Quenching38.22  91.06  53.67 
25.62  117.91  68.21 
450 & 600 (multi heat treatment)Annealing29.30  101.47  111.81 BHN60.09  65.365 RHN
37.00  123.64  70.09 
Quenching34.52  113.60  66.76 
31.31  108.51  64.52 
Unhardened & unpressed aluminum casting21.00  99.25    58.77   

The bold and underlined values are indicated that the better hardness values were obtained based on multi heat treatment process.

3.4Observation of NDT report

Nondestructive testing is used in a selection of settings that shields an extensive choice of an industrial activity, with new NDT methods and applications, being uninterruptedly established. Nondestructive testing methods are regularly functional in industries where a failure of a module would cause important hazard or financial loss, such as in transportation and pressure vessels.

In both annealing and quenching, the heat treatments were accomplished at the temperatures of 450 and 600°C. The heat treated specimens observed from the NDT results, there is no internal defects were observed because of added heat with the compressive effects of 400kN load used for the development of refined grain structure.

Here in this work each specimen has involved in to the radiographic examination of NDT testing. Separate films were utilized in the shape of 6cm×3cm for the readings taken. The interpretation of test results is showed no defects. It is noted that in Table 4 partial defects were identified in the non-heat treatable aluminum casting specimen through the Radio graphic test report. Otherwise there was not even single defects not identified during the heat treatable annealed and quenched specimen in both stages of observations. This can be confirmed with the microstructure representations as mentioned in Table 5. Following by hardness comparison, the good NDT outcomes will provide us clear solution and data comparison.

Table 4.

Nondestructive testing report of Al6061 casting samples.

S. No.  FT (°C)  W (kN)  Heat treatment  NDT observation 
600 (mono heat treatment)400AnnealingAcceptable 
Acceptable 
QuenchingAcceptable 
Acceptable 
450 & 600 (multi heat treatment)AnnealingAcceptable 
Acceptable 
QuenchingAcceptable 
Acceptable 
Unhardened & unpressed aluminum castingPartial 
Table 5.

SEM Micro structure remarks of particle size and grain boundary thickness (μm).

No.  FT (°C)  W (kN)  Heat treatment  t (mm)  Microstucture remarks
          Average particle size (μm)  Grain boundary thickness (μm) 
600 mono heat treatment400Annealing34.61  1.4061  76.48 
24.71  1.3678  73.29 
Quenching38.22  1.2265  72.04 
25.62  1.1693  71.40 
450 & 600 multi heat treatmentAnnealing29.30  1.1456  70.68 
37.00  1.3146  71.45 
Quenching34.52  1.4557  75.43 
31.31  1.5229  74.77 
Unhardened & unpressed aluminium casting21.00  2.2837  85.42 

The bold and underlined values indicates that the poor results (Particle size and Grain boundary thickness) of the untreated and uncompressed specimen.

3.5SEM identification of particle size and grain structure

It is very important that the microstructural readings were presented in Table 5. It represents the values of average particle size and grain boundary thickness in micro meters. The observed readings from the micro graphical structure used to identify the particle size measured through the Scanning Electron Beam microscope Vega-3 TESCAN as shown in Fig. 8.

The SEM images showed the detailed structural changes of both differentiated casting specimens. The highlighted samples were involved thorough the SEM inspection with the respective magnification factor level. For different image interpretation various readings were captured from the peripherals of the prepared specimen. Its grain boundary also noticed as 70.68μm as recorded from SEM images. Similarly, better particle size 1.1693μm were found during the quenching of mono heat treated primary stage of Al6061 casted samples.

The grain boundaries of many observations also got minimum during the multi heat treatable casted specimen. The reason behind these good bond strength and particle size are the change in thickness by hot compressed specimen by UTM pressing. Wherever the thickness got minimum because of hot pressing good results were found in particle size and grain boundary strength. Unhardened specimen had large sized particles and less grain boundary strengthening compare with the mono and multi heat treated specimens. The relationship between the SEM results and the specimens are mentioned in Fig. 9. The relationship of SEM readings and hot forming temperature described in Fig. 10 that the higher value of grain boundary thickness was identified for the unhardened specimen. Better particle size and gain boundary was obtained during the multi heat treated hot formed specimen. Uniform increments and peaks of particle size and boundary thickness were identified from these experiments.

4Conclusion

  • Defect less casting specimen were prepared successfully by the casting of pure Al6061 alloy material. Complete survival of material testing was accomplished by NDT method which explained that the hot forming heat treated samples thoroughly removed all the internal stresses and defects.

  • Hardness measurement helps to identify the ability to resist the loads among the various samples which is clearly agreed that more hardness is chanced in multi heat treated samples compare with the mono heat treated samples.

  • Displacement variation is minimum during the multi heat treated specimen inspection because of change in thickness varying depends on the heating temperatures at about 600°C. This was confirmed with the displacement values of dynamic simulation by Deform 3D forming tool.

  • The grain boundary thickness and particle size were recorded minimum due to the hot compressed multi heat treated Al6061 samples. The strain rate becomes high used to change the particle size minimum. This productive material processing applied in the field of aerospace applications and used in light weight high strength components

  • Better observations of particle size reduction, grain boundary strengthening and high hardness were acknowledged good in multi heat treated hot pressing of Al6061 casting samples. There were no more defects identified among the both mono and multi heat treated casting samples.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

The author(s) disclosed receipt of the following financial support for the research, authorship, of this manuscript, financial supports from the Tamil Nadu State Council for Science and Technology (TNSCST), DOTE Campus, Chennai, through the Fundamental Research Grant Ref. No. TNSCST/SPS/AR/2017-2018 are gratefully acknowledged.

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Copyright © 2019. Brazilian Metallurgical, Materials and Mining Association
Journal of Materials Research and Technology

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