Effect of solution time on microstructure and mechanical properties of Al-17Si-4Cu-0.5Mg alloy formed by semisolid squeeze casting

Abstract

The effects of hypereutectic Al-17Si-4Cu-0.5Mg alloy were prepared by semisolid extrusion. The effect of solution time on microstructure and properties of hypereutectic Al-17Si-4Cu-0.5Mg alloy was studied. Results show that spheroidization occurs in the Si phase with the increase of solution time. When the solution time reaches 10 h, the circularity of eutectic Si is 0.72. High concentration of Cu element is enriched around Si phase in as cast state. After solution for 1 h, Cu element is rapidly dissolved into the matrix. As solution time is increased from 1 h to 16 h, the diffraction peak intensity of θ(Al2Cu) and Q(Al5Si6Cu2Mg8) phases on the XRD curve is decreased, and the dislocation density in the alloy matrix is greatly reduced. After aging treatment at 180℃ is performed on the solution treated samples, the θ' and Q' phases precipitate. As the solution time increases, the alloy strength value shows a "double peak" phenomenon. After solution treatment for 1 h, the tensile strength of the alloy reaches 269 MPa and the yield strength is 233 MPa. Compared with the unheated alloy, they are increased by 43.3% and 42.7%, respectively. This is mainly because there is still larger dislocation density in the matrix at the initial stage of solution, and the precipitation has stronger pinning hindrance to the dislocation after aging treatment. When the solution time is 10 h, the tensile strength and yield strength of the alloy reach 311 MPa and 263 MPa, respectively. The roundness of Si phase and the strengthening effect of fine precipitates are the main reasons for the formation of the second strength peak.

Keywords

• solution time
• semisolid squeeze casting
• al-si-cu-mg alloy
• microstructure
• mechanical property