Cast A356 Research Articles

Effect of process parameters on tensile strength of friction stir welded cast A356 aluminium alloy joints

A356 is a high strength aluminium-silicon cast alloy used in food, chemical, marine, electrical and automotive industries. Fusion welding of this cast alloy will lead to many problems such as porosity, micro-fissuring, and hot cracking. However, friction stir welding (FSW) can be used to weld this cast alloy without above mentioned defects. An attempt was made to study the effect of FSW process parameters on the tensile strength of cast A356 aluminium alloy. Joints were made using different combinations of tool rotation speed, welding speed and axial force. The quality of weld zone was analyzed by macrostructure and microstructure analyses. Tensile strengths of the joints were evaluated and correlated with the weld zone hardness and microstructure. The joint fabricated using a rotational speed of 1000 r/min, a welding speed of 75 mm/min and an axial force of 5 kN showed a higher tensile strength compared to the other joints.

Influence of Different Pouring Temperature to Properties and Organization of A356 Aluminum Alloy under Specified Conditions

Due to the excellent casting performance, good corrosion resistance, high strength and casting manufacturing costs, A356 casting aluminum alloy is widely used in automobile wheel industry of China. However, for the restrictions of the production equipment, technology and the production craft level, there are problems that product quality is not satisfied and the production efficiency is low in the mass manufacturing. In this paper, the effect of pouring temperature and mold temperature on the microstructure and mechanical properties were investigated on the basis of cooperation project with Bin Zhou wheel hub manufacturing company. The quantitative relationship between mechanical properties and microstructure was studied by statistical methods. The results indicate that pouring temperature is the main element to affect the mechanical properties of permanent mold casting A356 and the optimum pouring process parameter is about 744 .Mechanical properties have a liner relationship with secondary dendrite arm spacing in a certain extent.

The semisolid microstructural evolution of a severely deformed A356 aluminum alloy

A cast A356 aluminum alloy was successfully processed through applying a new severe plastic deformation method, accumulative back extrusion (ABE), at the temperature of 300°C. In consequence, a severely deformed microstructure consisting of round and fine Si particles has been obtained. Microstructural evolution of the ABE-processed material soaked for various times at different isothermal temperatures in semisolid state was investigated. It has been shown that the proposed semisolid thermomechanical route would lead to a fine semisolid microstructure, where the spheroidal α-Al globules are surrounded by continuous liquid film. The results indicate that the ABE processing followed by 10min holding at 580°C and/or 6min at 590°C has led to the best thixotropic characteristics, i.e., the high shape factors and low globule sizes. The thixotropic structure characteristics have been also properly discussed in terms of globularization and coarsening mechanisms as well as the kinetics of microstructural evolutions. The almost linear semisolid coarsening behavior of the processed material indicates the outstanding role of Ostwald ripening mechanism in the growth of globules.

Artificial neural network modeling to predict the hot deformation behavior of an A356 aluminum alloy

Prediction of the material flow behavior is an essential step to optimize the design of any forming process. In this context, artificial neural network (ANN) may be used as a reliable modeling method for simulating and predicting the flow behavior of materials under different thermomechanical conditions. In the present study, an ANN model has been established to estimate the high temperature flow behavior of a cast A356 aluminum alloy. A series of isothermal compression tests was conducted in the temperature range of 400–540°C and strain rates of 0.001–0.1s−1. A feed-forward back propagation ANN with single hidden layer composing of 20 neurons was employed to simulate the flow behavior. The neural network has been trained using an in-house database obtained from hot compression tests. Finally, in comparison with a strain-dependent Arrhenius type constitutive equation, the reliability of the proposed ANN model has been evaluated using standard statistical indices. The results indicate that the trained ANN model is a robust tool to predict the high temperature flow behavior of cast A356 aluminum alloy.

The negative effect of solution treatment on the age hardening of A356 alloy

The effect of solution treatment on the age hardening of an A356 (Al–7.0Si–0.3Mg) alloy was investigated by hardness measurements and electron microscopy. This study presents experimental evidences that a prolonged solution treatment has a detrimental influence on age hardening due to the porosity in the cast A356 alloy. The enrichment of Mg on the internal surface of the porosity was observed. Nanoscale particles of magnesium oxides exist in the samples that have been solution treated with an extended duration. Our results indicate that Mg atoms would diffuse toward the porosity pre-existed in the A356 alloy during solution treatment. This phenomenon is consistent with the degraded aging kinetics and hardening potential of the A356 alloys solution treated for a long time, since the reduction of Mg solutes in the Al matrix shall lead to a decrease of the volume fraction of the Mg–Si-containing strengthening precipitates, which are mainly the monoclinic β″ phase. Our findings emphasize the significance of controlling porosities for the A356 alloys and may provide useful information for designing thermal treatment parameters to reach the optimum balance between strength and ductility.

Effect of ablation casting on microstructure and casting properties of A356 aluminium casting alloy

Recently the Ablation Casting Technology was invented as a new casting process to improve foundry products quality. In this study, the effects of processing variables on the porosity content, microstructure and feedability of A356 casting alloy were investigated. Secondary dendrite arm spacing (SDAS) and eutectic silicon morphologies were studied to evaluate the influence of Ablation Casting on the microstructure. Casting density was measured in order to identify porosity content and feedability of ablated and non-ablated specimens. In addition, solidification behavior of the samples was investigated by using thermal analysis technique. The cooling curves and the first derivative curves were plotted and compared with each other. Results showed the ablation process could increase solidification rate significantly. In addition, the microstructural evidences revealed that Ablation Casting process results in more fine and homogeneous structure compared to the nonablated casting. The feedability improved, SDAS reduced to 35% and porosity content decreased to 3.84 vol.% by implementing this process. It concluded the Ablation Casting is an effective process to gain higher quality in aluminum foundry.

Effects of the Mn/Fe Ratio and Cooling Rate on the Modification of Fe Intermetallic Compounds in Cast A356 Based Alloy with Different Fe Contents

Effects of the Mn/Fe Ratio and Cooling Rate on the Modification of Fe Intermetallic Compounds in Cast A356 Based Alloy with Different Fe Contents

Quantification of volume deficit of rectangle shaped cast aluminium alloys

Volume deficit of rectangular shape US 413 and US A356 cast aluminium alloy has been estimated in the present study. The decrease in specific volume directs to a volume deficit in castings and it has been shown as a defect. The volume deficit can be classified as macro cavities, internal porosity, surface sinking and volumetric contraction and measured using mathematical formulae; the actual volume deficit of the given casting was obtained by adding all the defects. Quantification of internal closed porosity has been addressed through X-ray computer tomography. The information regarding the volume deficit and its distribution is critical in minimizing casting defects.

Dynamic fracture toughness of Al–7Si–Mg (A357) aluminum alloy

Impact behavior related to crack initiation and growth of cast A357 (Al–7Si–0.7Mg) alloy was experimentally investigated. Dynamic fracture toughness for various artificial aging conditions were evaluated by exploiting instrumented impact Charpy V-notch experiments; impact tests were preferred instead of the standard fracture toughness tests in order to have a fast assessment of the effect of artificial aging on the fracture toughness behavior. Characteristic points of impact load–deflection curves related with cracking were identified and post-correlated with different artificial aging conditions. Absorbed impact energies for stable and unstable crack growth were calculated for 28 different aging conditions; resulting cracking velocity at the unstable crack regime (rebound compliance) was also calculated and it was found that rebound compliance is inversely related to ductility. Cracking initiation load values were identified by exploiting the compliance changing rate method; both stress intensity factor and J-integral analysis were employed to calculate critical dynamic fracture toughness values. They were found to be slightly higher than corresponding quasi-static properties and they are both changing with varying aging conditions. Limitations and results of both notch-fracture toughness analyses were discussed by taking into account the material aging condition. Performed scanning electron microscopy on the fracture surfaces revealed the fracture mechanism that is correlated with respective microstructure.

Fatigue Behavior of A356 Cast Aluminum Alloy Microstructurally Modified by Friction Stir Processing under Low Strain Rate Condition

The fatigue behavior of cast aluminum alloy, A356-T6, microstructurally modified by the friction stir processing (FSP) was investigated. The FSP conditions were set to be the tool rotational speed of 500 rpm and traveling speed of 200 mm/min, in which the strain rate was relatively low. Plane bending fatigue tests have been performed using the as-cast and friction stir processed (FSPed) specimens. Fatigue strengths in the finite life region and the fatigue limit of the FSPed specimens were highly improved compared with the as-cast ones resulting from the elimination of casting defects by the FSP. However, the crack growth rates of the FSPed specimens were faster than those of the as-cast ones due to the softening of the material by heat input during the FSP. The effects of FSP with low stain rate were discussed based on the microstructural consideration.

HRTEM and HAADF-STEM of precipitates at peak ageing of cast A319 aluminium alloy

High-resolution transmission electron microscopy (HRTEM) and high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM) were applied to investigate the precipitates formed during age hardening at 170±5°C for up to 48h of cast A319 aluminium alloy (Al–4.93wt%Si–3.47wt%Cu). The precipitates at the peak-aged condition have been identified as mainly θ” together with a smaller amount of θ’. It is proposed that the θ” is responsible for hardening at peak ageing at 170°C of the cast A319 aluminium alloy.

Microstructural Evolution of A356 Al Alloy During Flow Along a Cooling Slope

Cooling slope (CS) has been used in this study to prepare semi-solid slurry of A356 Al alloy, keeping in view of slurry generation on demand for Rheo-pressure die casting process. Understanding the physics of microstructure evolution during cooling slope slurry formation is important to satisfy the need of semi-sold slurry with desired shape, size and morphology of primary Al phase. Mixture of spherical and rosette shaped primary Al phase has been observed in the samples collected during melt flow through the slope as well as in the cast (mould) samples compared to that of dendritic shape, observed in case of conventionally cast A356 alloy. The liquid melt has been poured into the slope at 650 A degrees C temperature and during flow it falls below the liquidus temperature of the said alloy, which facilitates crystallization of alpha-Al crystals on the cooling slope wall. Crystal separation due to melt flow is found responsible for nearly spherical morphology of the primary Al phase.

Industrial Heat Treatment of R-HPDC A356 Automotive Brake Callipers

Heat treatment of rheo-high pressure die cast (R-HPDC) A356 brake callipers has produced good mechanical properties on the laboratory scale. An industrial heat treatment is required to evaluate the applicability and conformance of the R-HPDC A356 brake callipers to the automotive industry. This research studied A356 brake callipers heat treated on the industrial scale with particular emphasis on the resulting microstructure, hardness and tensile properties. The eutectic Si-particle spheroidisation after solution heat treatment was achieved and observed with optical microscopy. A hardness increase from 64 to 100 Vickers was achieved from the as-cast condition to the industrially heat treated T6 condition. The heat treatment caused no significant variation in hardness and tensile properties from brake callipers within the same batch or from different batches. The yield and ultimate strengths of the industrial heat treated brake callipers were lower compared to the laboratory scale heat treatment properties, while the ductility increased, mainly due to quenching effects. Even though the industrial heat treated A356 brake callipers resulted in yield and ultimate tensile strengths lower than those achieved on a laboratory scale, they still exceeded the minimum specifications for gravity die cast A356 brake callipers.

A357 Aluminium Cast Alloys for Extrusion Processes

The A357 Al-Si-Mg cast alloy is commonly used for cast production of automotive components in conventional HPDC and in semi-solid processes. The aim of this work is to study the application of A357 cast alloy in thixoextrusion processes. This technology offers new possibilities of application for cast alloys and several advantages in from of conventional processes of hot-extrusion: lower pressure, minor friction forces, higher material fluidity and longer tool life. The thixoextrusion was experimented in a pilot plant, at different speeds and temperatures, with an induction furnace and a 400 Tn press. With ingots of A357 as cast, a tool with a ratio of 8.5 and with temperatures of extrusion around 560 °C, it is possible to obtain extrusion speeds more than 3 m•s-1. In all cases, when the speed of extrusion increases, the press of extrusion decreases. The effect of heat treatments and extrusion speed in the microstructure of the extruded product is evaluated.

Severe plastic deformation of rheoforged aluminum alloy A356

In this research, the electromagnetic stirring (EMS) process was used to produce semi-solid slurry with globular structure from cast A356 aluminum alloy. Then the slurry was forged in a die, which named rheoforging process. Utilizing multidirectional forging (MDF), the effect of severe plastic deformation on microstructure and mechanical properties of this alloy in dendritic and globular states was investigated. Shear punch, micro- and macro-hardness tests were used to study the mechanical properties of these samples. For metallographic examinations, the optical microscope equipped with the Clemex® image analyzer software was used. Optimum globular structure of rheoforged specimens was achieved to deform those in three successful passes of MDF. The results show that more severe strain can be imposed on globular structure with respect to dendritic one. Also, MDF process can effectively improve the strength of the samples with no noticeable change in globules morphology of the rheoforged samples.

Modelling approach for quantitative prediction of macroshrinkage and microshrinkage in A356 sand mould castings

An advanced casting simulation based optimisation approach was applied in this study to assist in the improvement of the mould design of aerospace components made of A356 alloy. By using this approach, mould filling and solidification related defects (including macroshrinkage and shrinkage porosity) were significantly minimised and hence it helped in cost reduction, performance enhancement and quality assurance of complex A356 cast parts. An experimental validation and detailed calibration procedures of the models for prediction of macroshrinkage and shrinkage porosities were performed using A356 plates cast in furan–silica sand moulds using the Prometal rapid casting technology (RCT) mould printing technology. Correlations between Niyama values and the pore percentage were also developed. Therefore, the severity level of shrinkage porosity can be determined via the Niyama criterion. Predictions were then compared with the macroshrinkage and porosity measurements in plates of various plate thicknesses and in other commercial A356 casting components.

A Study on Surface Oxidation Coating Characteristic of Al-Si Casting Alloys

in this paper, it was aimed to improve understanding about the effects of physical melt treatment on the morphologies of eutectic silicon crystal size, and then the effects of these microstructural features on anodizing characteristics. A380 and A356 casting aluminum alloys were used in this experiment. A twin-screw melt-shearing process and an electro magnetic stirring process were utilized before high pressure die casting. In order to refine and homogenize the microstructure of the diecast Al-Si alloys, the melt-shearing process parameters were controlled and T6 heat treatment was carried out. A uniform microstructure over the whole thickness of the diecast specimens caused smaller difference in oxidation coating layer thickness between machined and non-machined surfaces. More uniform anodic coating layer was obtained by AC/DC coupled anodizing and PEO processes compared to conventional DC anodizing process.

NDE of friction stir welds of Al alloys using high-frequency acoustic microscopy

This paper presents results on high-frequency ultrasonic imaging of bonds between different materials with application to friction stir welding (FSW). The unique feature of this paper is the use of high numerical aperture lenses that allow the excitation of leaky surface acoustic waves. These interact with weak bonds to produce wave interference of incident and reflected waves at weak bond interfaces. The interference provides a vivid contrast marking the weak interface bond as an easily recognisable feature. Presented are a description of the high-frequency lenses, simulation of the contrast phenomenon and the application to friction stir welds. The welds were between cast A356 and wrought 6061 Al alloys obtained under four different processing conditions. The selected sections of these were imaged at high frequencies in the GHz range by bringing the acoustic lenses towards the specimen's surface far enough so that the peripheral lens rays were incident at large enough angles to exceed the first and second critical angles and to excite leaky surface acoustic waves. The interference of these waves allowed the imaging of the bond details with a resolution of about 1.5–3 μm. The features and flaws observed in the images were correlated with those reported on in the literature as well as those obtained from scanning electron microscopy and tensile property evaluation. The quality of weld bonds inferred from the images was correlated to the tensile fracture experiments, which showed that improperly bonded specimens showed a relatively larger number of flaws. The results suggest that high-frequency acoustic microscopy is indeed a useful method for the diagnostic evaluation of FSW, especially since acoustic microscopes are now available as portable instruments commercially.

The effect of thermomechanical parameters on the eutectic silicon characteristics in a non-modified cast A356 aluminum alloy

Abstract The influence of hot working parameters on the microstructural evolution of cast A356 aluminum alloy has been studied emphasizing the changes in eutectic phase morphology. Toward this end, a set of isothermal compression tests were conducted in the temperature range of 400–540 °C. The results indicate that the eutectic Si platelets are fragmented, spheroidized and also evenly distributed in the matrix as a result of applying proper thermomechanical cycles. The mechanical fragmentation and thermal disintegration play a prominent role in Si particles breaking up under the different deformation conditions, whereas the average particle size is decreased with decreasing the temperature and increasing the strain rate. The lowest shape factor and aspect ratio are also achieved for the specimens deformed at higher temperatures and lower strain rates. The current work also explores the high temperature flow behavior of cast A356 alloy to address the dominant restoration processes taken place at different thermomechanical conditions.

Wear of Al–Si alloys matrix reinforced with sol–gel coated particles

In the present study, squeeze cast A356 matrix composites reinforced with coated B4C particles were fabricated. Attempts were made to coat the B4C powders with TiB2 via a sol–gel process and incorporate them into the A356 alloy by a mechanical stirrer. The hardness of B4C particle is the third highest among all materials of this type. The wear properties of unreinforced A356 alloy and composites with different volume percentages of coated boron carbide particles were experimentally investigated. It is noted that composites exhibit better wear resistance compared to unreinforced alloy. The presence of B4C particles could shield the matrix and silicon phases from directly experiencing the applied load and reduce the weight loss during the wear test. According to the differences in wear rates of the composites, two separate wear rate regimes were identified as low and high wear rate regimes. Microscopic examination by a scanning electron microscope equipped with an energy dispersive spectrometer has also been carried out on the worn surfaces and debris.