Rheo-diecasting Process Research Articles

Microstructure and Mechanical Properties of a Rheo-Diecast Mg–10Zn–4.5Al Alloy

High zinc content Mg–Zn–Al alloys have the potential to be used as high pressure die casting (HPDC) alloys for applications up to 150C. However, these alloys show high tendency to hot tearing and microporosity. Rheo-diecasting (RDC) is an innovative semisolid HPDC process, which can effectively eliminate the formation of primary magnesium dendrites and convert them into fine, globular particles. This very positive change in the morphology and distribution of the primary phase reduces the subsequent formation of various casting defects. In this study, a composition of Mg–10Zn–4.5Al was selected from the Mg–Zn–Al system and processed with both HPDC and RDC. It is shown that, samples produced by the RDC process exhibit substantially reduced hot cracks, few gas pores, and a nearly uniform distribution of fine, globular primary particles. These microstructural changes resulted in much improved strength and elongation, which are comparable to those of AZ91D, while the processing temperature is much lower. It is concluded that high zinc content Mg–Zn–Al alloys have good potential to be exploited as commercially useful alloys by the RDC process.

Performance of semi-solid slurry produced by twin-screw stirring mixer and rheo-diecasting process of AZ91D alloy

The microstructure of semi-solid slurry of AZ91 D alloy, which was produced by twin-screw stirring mixer under the different parameters, was investigated. Rheoforming by cold chamber die casting process was performed thereafter. The results indicate that with decreasing of the barrel temperature of the mixer and the pouring temperature of molten Mg alloy, the solid fraction of semi-solid slurry increases and the size of non-dendritic grains becomes smaller. While the shear rate increases, the solid fraction of semi-solid slurry decreases. The tensile strength and elongation of metal rheoformed by die casting are higher by about 37% and 44% respectively than those produced by conventional liquid die casting.

Study on a Semi-Solid Rheo-Diecasting Process With AZ91D Alloy Slurry

In this paper, a rheo-diecasting process of AZ91D alloy semi-solid slurry produced with a twin-screw stirring mixer was investigated. The results show that the tensile strength and elongation of the sample made by rheo-diecasting were 37% and 44% higher, respectively, than those produced by conventional liquid diecasting. The castings fabricated by rheo-diecasting possessed good density with low shrinkage and could be heat treated. It is a “near-net shape” production process.