Application of Rheo-diecasting of a High Strength Al^|^ndash;Si^|^ndash;Mg Alloy to Automotive Suspension Arms

Abstract

A rheo-diecasting using a high-strength Al alloy has been investigated to estimate its applicability to the manufacturing of automobile suspension parts to replace the hot-forging process. The alloy used in the present study was based on the Al-Si-Mg system, which was developed recently for high mechanical performance in rheo-diecasting. Two important aspects were considered in this effort to use rheo-diecasting in practical applications: (i) optimization of the manufacturing conditions for semi-solid slurries and (ii) a proper mold design for rheo-diecasting. Electromagnetic stirring of the melt was carried out to obtain high-quality slurries. Two types of gating systems were considered: the vertical gate type and the horizontal gate type. A horizontal type of gating system with an injection velocity of 0.5-1.5 m/s, as designed using computer simulation of the fluid flow, was successfully applied to the rheo-diecasting of tension arms. X-ray inspection and microstructure observation were carried out to analyze the formation of casting defects. No defects, such as shrinkage porosity and eutectic segregation, were found in the rheo-diecast products. An evaluation of the rheo-diecast tension arms was carried out through a tensile test, a durability test and assembled module tests. The rheo-diecast products showed significant improvements in their tensile properties, such as the yield strength of 281 MPa, the tensile strength of 331 MPa, and the elongation of 11.8%, which are superior to those values of high pressure diecasting products. In the durability and assembled module tests, the rheo-diecast tension arms satisfied the specifications of hot-forged tension arms.