Effect Of Hyper-Eutectic Al-Si Alloy On Microstructure And Mechanical Properties By Squeeze Casting

Hyper-eutectic Al-Si alloy has a series of advantages, such as small specific gravity, good abrasion resistance, good corrosion resistance, low expansion coefficient and excellent casting forming and processing properties. But this alloy also have some shortcomings, which make the performance becomes poor, especially toughness, for example primary silicon phase appears with bulky platelet and eutectic silicon phase appears with needle flake or lath-shaped. However, the microstructure will be changed and the performance will be improved by squeeze casting.The microstructure of multiple hyper-eutectic Al-17.5%Si alloy metal mould gravity casting include bulky and sharp edges and corners of primary silicon phase and Al-Si-Mn-Fe-Cr-M o phase, then the needle of Al 2 Cu phase, the clubbed of Mg2Si phase and eutectic silicon phase will dissever the matrix while loading in. With the specific pressure increasing, the microstructure of multiple hyper-eutectic Al-17.5%Si alloy casting was composed with many of primaryα-Al dendrites, which is more and more fine and dense; primary silicon phase, the size is very small, about 25μm and the distribution is also very evenly; eutectic silicon phase and other second phases has also been refined. Under 220 MPa, the mechanical properties of squeeze casting is the best, at room temperature, the tensile strength is 188.5 MPa and the elongation at break is 4.50%; at high temperature, the tensile strength is 173.25MPa and the elongation at break is 4.75%; After T6 heat treatment, at room temperature, the tensile strength is 255.95MPa and the elongation at break is 4.77%.In order to researching the effect of specific pressure on the microstructure and properties of hyper-eutectic Al-17.5%Si alloy, the material that binary hyper-eutectic Al-17.5%Si alloy could be carried out the squeeze casting experiment. With the specific pressure increasing, the microstructure of binary hyper-eutectic Al-17.5%Si alloy casting was also made up of many of primaryα-Al dendrites, which is more and more fine and dense; the size of primary silicon phase is very small and the number is less and less; eutectic silicon phase has also been refined. This result also can be got by X-ray diffraction analysis. The mechanical properties of squeeze casting under 940MPa with no modification treatment is that the tensile strength is 153.33MPa and the elongation at break is 10.76% at room temperature; The mechanical properties of squeeze casting under 1100 MPa with Sr modification treatment is that the tensile strength is 203.33MPa and the elongation at break is 11.66% at room temperature. Compared to the metal alloy of as-cast, mechanical properties are further improved too.Besides, the plastic property of the binary hyper-eutectic Al-17.5%Si alloy casting can be improved obviously by squeeze casting after hot extrusion and this alloy became easy to deformation. In the meantime, primary silicon phases and eutectic silicon phases take place further broken, and then The mechanical properties also increase a lot. The billet is made from 260MPa by squeeze casting have good mechanical properties after hot extrusion, the hardness can be up to HB 70, higher. than that of squeeze casting. The mean diameter and morphology of silicon particles that the binary hyper-eutecticAl-17.5%Si alloy casting by squeeze casting could be controlled by the temperature and time of homogenizing treatment. The optimal temperature and time of homogenizing treatment is 535℃and 24 h which get through the experiment. According to the literature, At the same time, with the temperature rising and the time extension of homogenizing treatment, the hardness of this alloy gradually declined, and then tend to be gently.