Preparation Of High-performance And Wear-resistance Of Hypereutectic Al-Si Alloy

Hypereutectic Al-Si alloy with the quality of high hardness, low linear expansion coefficient, good wear resistance and low density, is ideal for automotive piston materials. However, this type of alloy has some shortcomings, which diminish its properties, particularly toughness. For example, a primary Si phase can appear with a bulky platelet, and the eutectic Si phase can appear with a needle-type flake or lath-shaped morphology. Currently, improving the morphologies of primary Si and eutectic Si are the key point of research about the application of hypereutectic Al-Si at home and abroad. This test adopted different forming technologies and heat treatment methods to improve the microstructure and intensify the mechanical properties of alloy.The effects of electromagnetic stirring, ultrasonic melt treatment and squeeze casting on microstructure and mechanical properties of hypereutectic Al-Si alloy were investigated. It found that the three methods all could improve the microstructure and mechanical properties of alloy. However, the effect of squeeze casting on microstructure and mechanical properties of alloy was more obvious when compared with the other two methods. The amount of fine primary α-Al dendrites increased with an increase in applied pressure during solidification. However, this led to a reduction in the primary Si phase. The alloy had the better comprehensive mechanical properties and the brinell hardness of 66.8HB had increased 12.08%, the tensile strength of 153 MPa had increased 31.90% and the elongation of 5.25% had enhanced 173.44% at the pressure of 598 MPa.The changes of the microstructure and mechanical properties of hypereutectic Al-xSi under the same pressure during the process of solidification were investigated. The number and the size of primary Si phase were increased and the amount of primary α-Al dendrites was decreased in the microstructure of alloy with the raise of the Si content. After squeeze casting, the mean diameter of primary Si particles of hypereutectic Al-(15, 17.5, 22)Si alloy reduced to 5.59μ m, 9.22μ m and 14.30μ m, respectively. The wear loss of alloy was decreased with the increase of Si content and the wear resistance of hypereutectic Al-22 Si alloy was better. A wear loss of 4.9mg and a friction coefficient of 0.3151 were obtained of squeeze casting hypereutectic Al-22 Si alloy at 598 MPa.The effects of homogenization time on microstructure and mechanical properties of hypereutectic Al-Si alloy were investigated in the article. With the increase of homogenization time, the morphology of Si phase was more rounding. Consequently, the mechanical properties of alloy were improved obviously. The alloy had the well comprehensive properties when the homogenization time reached up to 12 h, and a brinell hardness of 54.5HB, a tensile strength of 142 MPa, an elongation of 11.4%, a wear loss of 6.5mg and a friction coefficient of 0.3231 were obtained after the squeeze casting of Al-Si alloy homogenized at 535℃ for 12 h.