Research On Microstructures And Properties Of Modified A356 Aluminum Alloy In Lost Foam Casting Process

The Lost Foam Casting (LFC) is considered as"the 21st century new casting technique"and"the green casting project"because of its unique advantages, such as high precision size, simple production process and low materials cost. However, the LFC defects of aluminum alloy including coarse grains, serious pinholes and low properties greatly limit the development of LFC aluminum alloy technology. It seems especially important to improve the microstructure of LFC aluminum alloy and enhance its properties. This research attempts to reach above objects by adding alloying elements to A356 alloy in LFC process.In this paper, the influences of La-Ce Rare Each (RE) and Mg modification on the microstructures and properties of A356 aluminum alloy in LFC were investigated, by the means of scanning electron microcopy (SEM) with energy dispersive X-ray analyses (EDAX), X-ray diffraction (XRD), Differential Scanning Calorimeter (DSC) and tensile testing. On the basis, the T6 heat treatments process of modified A356 aluminum alloy in LFC was studied.Adding a certain amount of RE(≤0.3%) to A356 aluminum alloy in LFC can effectively refine the grain and play a role of modification, which can change the shape of eutectic silicon from coarse plate-like into small granular or short sticky, thus significantly improve the ductility of A356 aluminum alloy. When the addition amount of RE is 0.3%, the tensile strength of the alloy increased by 17%, from 138MPa to162MPa. The elongation increased by 118%, from 6.1% to 2.8 %. However, the strength and elongation of the alloy declined when the addition amount of RE is more than 0.3%. Adding RE to A356 aluminum alloy in LFC could reduce the porosity of the alloy significantly. When the addition amount of RE is 0.3%, the porosity of the alloy decreased from 1.15% to 0.13%.Increasing the content of Mg in A356 aluminum alloy can significantly increase the tensile strength of the alloy in LFC, while decreasing the elongation of the alloy. When the addition amount of Mg is about 0.6%, the A356 aluminum alloy in LFC had optimal mechanical properties, and the tensile strength and elongation was 175MPa and 2.6%, respectively.The pinhole was significantly reduced, and the organization was refined by adding 0.3% RE to the modified A356+0.6%Mg alloy. The tensile strength and elongation of the modified alloy A356+0.6% Mg+0.3% RE in LFC reached 179MPa and 4.9%, respectively. The heat treatment process(T6) of the modified alloy A356+0.6%Mg+0.3% RE in LFC was studied and results shows that, the optimal T6 heat treatment process is solid solution at 538℃for 12 h, and then aging at 165℃for 6 h. After T6 heat treatment process, the maximum tensile strength and elongation of the modified alloy A356+0.6%Mg+0.3%RE in LFC could reach 327MPa and 3.1%, respectively.