Cast A356 Research Articles

Study on Defects of A356 Aluminum Alloy Wheel

This paper studied the effects of inclusion and slag on properties of a die cast A356 alloy wheel. The result showed that the rate of defect is important for the mechanical properties. The tensile strength and extension was not dropped but the rate of defect is increased about 2%. The variation trend of tensile strength and extension is linear, while the area of porosity on tensile fracture is between 2% and 6%. However, the tensile strength and extension was dropped with the increasing rate of defect. The variation trend of mechanical properties of the sample with inclusion is stable, but the sample with slag is not stable. The mechanical properties of samples with inclusion are drastically changed, while the rate of defect is increased. The mechanical properties of samples with slag are smoothly. The EDS analysis indicated that the defects consist of Al-Ti-B compound, α-phase (Al12FeSi), β-phase (Al9Fe2Si2) and Al2O3. These oxides form the compact composite oxide film expand into first cracks. The fracture mode of sample with defects is brittle fracture. The values of the Secondary dendrite arm spacing (DAS) in the inclusion and the matrix are the same, while the values of DAS in the slag and the matrix are different.

Prediction of Mechanical Properties of Cast A356 Alloy as a Function of Microstructure and Cooling Rate

Prediction of Mechanical Properties of Cast A356 Alloy as a Function of Microstructure and Cooling Rate

Effects of high-temperature solutionizing on microstructure and tear toughness of A356 cast aluminum alloy

Effects of high-temperature solutionizing on microstructure and tear toughness of A356 cast aluminum alloy

Effects of High-Temperature Solutionizing on Microstructure and Tear Toughness of A356 Cast Aluminum Alloy

A356 alloy was cast into permanent molds and subjected to T6 heat treatment. Two solutionizing (solution heat treatment) temperatures (540°C and 560°C) were used, with the holding time for each varied between 0 min and 240 min. Tear test specimens of 4 mm in thickness were machined from the castings. Tear toughness (UEp: unit crack propagation energy) was obtained from load-displacement curves. With increasing solutionizing holding time, eutectic silicon particles were found to become larger and mean interparticle distance was found to increase. The UEp of specimens solutionized at the higher temperature (560°C) increased with holding time until 120 min but decreased with longer holding times. SEM observation of fracture surfaces after tear testing revealed dimples originating from dispersed silicon particles within the eutectic phase. Fine dimples were also observed in the eutectic aluminum region in specimens with reduced UEp. These fine dimples were different from the dimples found to originate from the eutectic silicon particles.

Influence of Ti, B and Sr on the microstructure and mechanical properties of A356 alloy

In the present investigation, the microstructural and mechanical properties study of A356 alloy have been discussed. The microstructural aspect of cast A356 alloy employed in the present study is strongly dependent on the grain refinement (Ti and B) and modification (Sr). The mechanical properties such as PS, UTS, %E, %R, YM and VHN have been investigated. This paper deals with the combined effect of grain refinement and modification, which improves the overall mechanical properties of the alloy. It is also a well-known fact that the mechanical properties of cast A356 alloy were improved by subjecting suitable melt treatment such as grain refinement, modification and mould vibration, etc. The quality of castings and their properties can be achieved by refining of α-Al dendrites in A356 alloy by means of the addition of elements such as Ti and B which reduces the size of α-Al dendrites, which otherwise solidifies with coarse columnar α-Al dendritic structure. In addition, modification is normally adopted to achieve improved mechanical properties. Metallographic studies reveal that the structure changes from coarse columnar dendrites to fine equiaxed ones on the addition of grain refiner and further, plate like eutectic silicon to fine particles on addition of 0.20% of Al–10Sr modifier. The present result shows that a reduction in the size of α-Al dendrites, modification of eutectic Si and improvement in the mechanical properties were observed with the addition of grain refiner Al–3Ti, Al–3B and modifier Al–10Sr either individual addition or in combination. The change in the microstructure from coarse columnar α-Al dendrites to fine equiaxed dendrites and plate like eutectic silicon to rounded particles leads to improved mechanical properties.

Electron Back Scattering Diffraction Analysis of A357 Alloy Modified by Sr

Microstructure of A357 alloy modified by Sr has been investigated by the Electron Back Scattering Diffraction (EBSD) mapping technique using a Field Emission Gun Scanning Electron Microscopy (FEG-SEM). An appropriate sample preparation technique by ion milling was applied to obtain a sufficiently smooth surface for EBSD mapping. Results show that the eutectic morphology in microstructure of A357 alloy modified by Sr was changed to fine fibrous, and the grain size was refined. By comparing the orientation of the aluminum in the eutectic to that of the primary aluminum dendrites, the nucleation and growth mechanism of the eutectic solidification in A357 cast alloy was determined. The eutectic Si phase of the modified sample nucleates on the heterogeneous nuclei located in the region between primary α-Al dendrites and grows up, while the eutectic Si phase of the sample without modification nucleates on the primary α-Al dendrites and grows up.

Enhancement of wear and corrosion resistance of cast A356 aluminium alloy using friction stir processing

The present work pertains to investigation carried out on the feasibility of locally modifying the surface properties of cast aluminium alloy A356 using friction stir processing (FSP). The friction stir processed zone was characterized by metallography, electron micro probe analysis, hardness, dry sliding wear and potentio dynamic polarization testing. Hardness mapping showed that stir zones experienced increase of 40% compared to the as-cast metal. Further uniform micro-hardness was observed in the friction stir processed zone, which was not the case with as-cast A356 aluminum alloy. The FSP of cast A356 alloy exhibited excellent wear resistance, which is attributed to break-up of the coarse silicon rich eutectic particles, dendrite structure and homogenous distribution of fine Si particulates throughout the α-Al matrix due to intense plastic deformation and mixing during friction stir processing. The friction stir processed zone was also found to have adequate corrosion resistance. This work demonstrates that friction stir processing is an effective strategy for enhancement of wear and pitting corrosion resistance of as cast aluminum alloys

Experimental investigation for fatigue strength of a cast aluminium alloy

Fatigue strength of a type A319 cast aluminium alloy was studied by means of fully reversible tension–compression tests conducted at room temperature and at 130°C; the specimens used in this study came from samples cut from the bulkheads of V-8 type engine blocks. Testing was carried out in a servohydraulic machine following staircase schedules. The specimens were tested to fracture or up to 107 cycles. Analyses of the fatigue tests yield to a strength of 99.4 and 90.3MPa at 107 cycles for the tests at room temperature and at 130°C. The size and nature of the defects that originated the failure were determined by scanning electron microscopy. It was found that fatigue cracks originated in pores; single cracks were observed to occur in samples tested below a nominal reversible stress of 120MPa; multiple cracks were observed in samples stressed above this value.

Application of shortened heat treatment cycles on A356 automotive brake calipers with respective globular and dendritic microstructures

Since the automotive industry has many possible applications for semi-solid metal (SSM)-high-pressure die casting (HPDC) parts, the newly developed heat treatment cycles, as well as the traditional heat treatment cycles, were applied to A356 brake calipers cast using a LK DCC630 HPDC machine. Vickers hardness measurements at a cross section of the brake calipers were performed, indicating that similar values can be obtained when using the significantly shorter heat treatment cycles. Finally, the typical tensile properties that can be obtained for SSM-HPDC A356 brake calipers are compared with those manufactured by gravity die casting. Results indicate that the differences in microstructures (globular or dendritic) do not have a noteworthy effect on the heat treatment response. This implies that the short heat treatment cycles originally developed for globular SSM-HPDC A356 castings can be successfully applied to dendritic liquid A356 castings too.

Precipitation hardening of cast Zr-containing A356 aluminium alloy

The effect of small additions of zirconium on the hardness, grain size, precipitate type and size of cast A356 aluminium alloy was investigated. The cast alloys were solution treated and then artificially aged for different periods of time. Hardness tests and scanning electron microscope (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) studies were carried out on the as-cast, as-solutionised and age-hardened specimens. Incoherent, coarse Al 3Zr particles formed in the microstructure during the solidification of the alloy and caused grain refinement in the as-cast structure. These particles dissolved and reprecipitated as smaller-size particles during the solution treatment, causing the hardness of the alloy to remain constant at high temperatures for long periods of time due to the slow diffusion of Zr in the α-Al.

Friction stir welding of dissimilar A319 and A356 aluminium cast alloys

In the present investigation, the microstructure and mechanical characteristics of dissimilar A319 and A356 cast Al alloys plates joined by friction stir welding (FSW) were evaluated. The effect of tool rotational and welding speeds as well as the post-weld heat treatment (PWHT) on such properties was investigated. Post-weld heat treatment was carried out at a solutionising temperature of 540°C for 12 h followed by aging at 155°C for 6 h. For the as welded specimens, the welded zone (WZ) exhibited higher hardness values when compared with the A319 and A356 parent alloys. The peak hardness at the WZ was found to increase by increasing the tool rotational speed and/or reducing the welding speed. In contrast, the post-weld heat treated (PWHTed) specimens exhibited lower hardness values at the WZ than the parent alloys. For PWHTed specimens, the peak hardness at the WZ was found to decrease by increasing the tool rotational speed and/or reducing the welding speed. Tensile tests results demonstrate that, for the as welded specimens, the tensile fracture took place on A356 side where the hardness was minimal. While for PWHTed specimens, the fracture took place at the WZ. Increasing the tool rotational speed reducing both tensile and yield strengths, but increases the ductility of the joint.

Microstructure and Corrosion Behavior of Cast A356 and Wrought AA6061 Aluminium Alloy Welds

In this work, it was intended to improve the corrosion resistance of welds of A356 and AA6061 by adopting mainly a special welding techniques, viz., pulsed current gas tungsten arc welding (PCGTAW), electron beam welding (EBW) and friction stir welding (FSW). It was found that the corrosion resistance of A356 and AA6061 welds could be improved by PCGTAW technique rather than continuous current gas tungsten arc welding (CCGTAW). It can be further improved by using electron beam welding. Improved corrosion resistance in A356 welds could be obtained by selecting T6 temper rather than as cast condition. In the case of AA6061, improved corrosion resistance was achieved by selecting T4 temper rather than T6 temper. As for as the welding techniques, friction stir welding (FSW) is useful than fusion welding techniques like CCGTAW,PCGTAW and EBW for improving the corrosion resistance of both the welds.

Establishing relationship between the base metal properties and friction stir welding process parameters of cast aluminium alloys

In friction stir welding (FSW), the material under the rotating action of non-consumable tool has to be stirred properly to get defect free welds in turn it will improve the strength of the welded joints. The welding conditions and parameters are differing based on the mechanical properties of base materials such as tensile strength, ductility and hardness which control the plastic deformation during friction stir welding. The FSW process parameters such as tool rotation speed, welding speed and axial force, etc. play a major role in deciding the weld quality. FSW Joints of cast aluminium alloys A319, A356, and A413 were made by varying the FSW process parameters and the optimum values were obtained. In this investigation, empirical relationships are established and they can be effectively used to predict the optimum FSW process parameters to fabricate defect free joints with high tensile strength from the known base metal properties of cast aluminium alloys.

HRTEM and ADF-STEM of precipitates at peak-ageing in cast A356 aluminium alloy

Precipitates at peak-ageing in an A356 Al–Mg–Si alloy cast by a semi-solid process have been studied by high-resolution transmission electron microscopy (HRTEM) and annular dark-field scanning transmission electron microscopy (ADF-STEM). The major precipitate (ppt) at peak-ageing is the monoclinic β″ or pre-β″. Its orientation relationship with the fcc-Al matrix is [0 0 1] Al//[0 1 0] ppt, ( 0 2 0 ) Al / / coincide ( 6 0 1 ) ppt and ( 2 0 0 ) Al / / coincide ( 4 ¯ 0 3 ) ppt , equivalent to [0 0 1] Al//[0 1 0] ppt, ( 1 ¯ 3 0 ) Al / / ( 1 0 0 ) ppt and (3 2 0) Al//(0 0 1) ppt. The habit direction of this precipitate is [0 0 1] Al//[0 1 0] ppt forming facet planes on ( 1 ¯ 3 0 ) Al / / ( 1 0 0 ) ppt and (3 2 0) Al//(0 0 1) ppt, in which very good atomic matching was found. The contrast of the precipitate in ADF-STEM is reversed to the typical atomic number contrast. To understand such contrast, a dynamical simulation based on the multi-slice method was therefore performed using different atomic stacking models and successfully explain the reverse contrast of the experimental images of the precipitate.

Impact properties of the aircraft cast aluminium alloy Al-7Si0.6Mg (A357)

The impact mechanical properties of the widely used in the aeronautics A357 cast aluminum alloy were investigated by exploiting experiments on an instrumented Charpy impact testing machine. The evaluated impact properties for 25 different artificial aging heat treatment conditions were analyzed and discussed in conjunction with the respective tensile properties. Correlations are proposed to establish useful relationships between impact resistance and tensile strain energy density properties. The established correlations, which are well supported by the performed experiments, can be used to estimate the tensile ductility and toughness of the A357 cast aluminum alloy from the Charpy impact test. Performed fractographic analyses were supporting the physically arbitrary correlation between tensile strain energy density and impact resistance.

Influence of temper condition on microstructure and mechanical properties of semisolid metal processed Al–Si–Mg alloy A356

The microstructures and mechanical properties of strontium modified semisolid metal high pressure die cast A356 alloy are presented. The alloy A356-F (as cast) has a globular primary grain structure containing a fine eutectic. Solution treatment results in spheroidisation of the eutectic silicon particles under the T4 and T6 temper conditions. The A356-T5 maintains the fibrous silicon morphology after artificial aging. A356-T4 has better ductility and impact strength than A356-T5 due to its spheroidised silicon morphology. The impact properties of semisolid metal high pressure die cast A356 are controlled mainly by the silicon morphology and alloy strength (hardness), whereas tensile strength is determined by the degree of solid solution coupled with precipitate formation during aging.

Microstructural Inclusion Influence on Fatigue of a Cast A356 Aluminum Alloy

We examine the dependence of fatigue properties on the different size scale microstructural inclusions of a cast A356 aluminum alloy in order to quantify the structure-property relations. Scanning electron microscopy (SEM) analysis was performed on fatigue specimens that included three different dendrite cell sizes (DCSs). Where past studies have focused upon DCSs or pore size effects on fatigue life, this study includes other metrics such as nearest neighbor distance (NND) of inclusions, inclusion distance to the free surface, and inclusion type (porosity or oxides). The present study is necessary to separate the effects of numerous microstructural inclusions that have a confounding effect on the fatigue life. The results clearly showed that the maximum pore size (MPS), NND of gas pores, and DCS all can influence the fatigue life. These conclusions are presumed to be typical of other cast alloys with similar second-phase constituents and inclusions. As such, the inclusion-property relations of this work were employed in a microstructure-based fatigue model operating on the crack incubation and MSC with good results.

On the role of process variables in the friction stir processing of cast aluminum A319 alloy

The surfaces of cast A319 alloy plates of nominal composition (wt.%): Al – 5.2 Si – 2.51 Cu were subjected to single stir Friction Stir Processing (FSP) with a view to decreasing the grain size and porosity level and improving the mechanical properties. Three traverse feed rates and five tool rotational speeds were employed. For certain combinations of the variables, the processed alloy displayed an increase in value of around 50% in tensile strength and 20% in microhardness compared with those of the as-cast alloy. The ductility of the processed alloy had increased by a factor which ranged from 1.5 to 5. Optical and scanning electron microscopy revealed that FSP reduces the size of the second phase particles, which contributes to the improvements in mechanical properties.

Improving sliding and abrasive wear behaviour of cast A356 and wrought AA7075 aluminium alloys by plasma electrolytic oxidation

An important limitation of aluminium alloys for mechanical applications is their poor tribological behaviour. In this study, surface treatment by plasma electrolytic oxidation (PEO) has been applied to two widely used aluminium alloys: A359 (hypoeutectic Al–Si–Mg) cast alloy and AA7075 (Al–Zn–Mg–Cu) wrought alloy, in order to improve their wear resistance, under sliding and abrasive wear conditions. The main aim of this work was the comparison of the properties and wear resistance of the oxide layers grown under the same PEO treatment conditions on two different aluminium alloys which might be coupled in engineered components. Significant differences in the phase composition, microstructure and mechanical properties measured by microindentation were observed in the oxide layers grown on the two substrates, and were ascribed to the effects of the different compositions and microstructures of the substrate alloys. Abrasion tests were carried out in a micro-scale abrasion (ball-cratering) test, with both alumina and silicon carbide abrasive particles. The results demonstrated the influence of the abrasive material on wear behaviour: whereas relatively aggressive SiC particles gave comparable results for both PEO treated and untreated samples, with the less aggressive Al 2O 3 abrasive the wear rates of the PEO treated samples, for both substrates, were significantly lower than those of the untreated substrates. In unlubricated sliding the PEO treatment significantly increase the wear resistance of both the aluminium alloys, at low applied load. In this condition the wear behaviour of the PEO treated alloys is strongly influenced by the stability of a protective Fe–O transfer layer, generated by wear damage of the steel counterpart. Under high applied loads however, the transfer layer is not stable and the hardness of the PEO layer, as well as the load bearing capacity of the substrate, become the main factors in influencing wear resistance.

Correlation between ultimate tensile strength and solidification microstructure for the sand cast A357 aluminium alloy

Many studies have demonstrated a relationship between secondary dendrite arm spacing (SDAS) and the mechanical behaviour of cast aluminium–silicon alloys, both for tensile and fatigue strength. SDAS is related to the solidification time and can be predicted, with a good approximation, by finite-element simulation. However, other microstructural features can affect the tensile behaviour of cast aluminium alloys such as size and morphology of the eutectic Si particles, grain size, composition and morphology of the intermetallic compounds. The present investigation was aimed at finding valuable relationships between ultimate tensile strength and the previously mentioned microstructural parameters for the sand cast A357 aluminium alloy. The microstructural characterization was carried out by optical microscopy and image analysis on more than about 2500 micrographs. Starting from the microstructural parameters and taking into account the material hardness, a relationship able to predict the ultimate tensile strength of the alloy, with an error less than 5%, was found. This relationship can be used to evaluate the local values of the UTS in complex cast components knowing only the hardness and the microstructural parameters, even in positions where the extraction of tensile specimens is not possible.