Investigation On Microstructure And Mechanical Properties Of Rheo Die-Casting For Semi-Solid AlSi9Mg Alloy

The greatest advantage of semi-solid rheological forming process is that process flow short, low production costs, in line with the requirements of energy-saving and emission reduction. In recent years it has become a trend of semi-solid forming technology. Use of semi-solid alloy melt with thixotropic characteristic semi-solid rheo-die casting can effectively reduce or eliminate the porosity defects. Semi-solid rheo-die casting has unique advantages and its industrial application is very promising.In this paper, semi-solid AlSi9Mg alloy melt prepared by sloping plate. Then rheo-die casting and made it to standard samples. Pouring temperature, injection pressure, injection speed and parameters of solution heat treatment process are studied. Find how they affect the microstructure and mechanical property on AlSi9Mg semi-solid alloy. Microstructure evolution of the primary solid phase is analysed along alloy melt filling process.The experiments show that: pouring temperature have great influences on the microstructure of semi-solid AlSi9Mg alloy melt. In this experiment, suitable pouring temperature is 610~615℃. When pouring temperature is 615℃the primary solid fraction is 40.3%, the average diameter of primary solid phase is 22.4μm, roundness is 0.606.Injection pressure has great influences on the microstructure and mechanical properties of semi-solid AlSi9Mg alloy. In this experiment, suitable injection pressure is 48~72MPa. When injection pressure is 48MPa, the tensile strength of the sample is 233MPa, elongation percentage is 4.5%, Brinell hardness is 76, and impact toughness is 98kJ?m-2. In microstructure the primary solid fraction is 27.3%, the average diameter of primary solid phase is 17.2μm, roundness is 0.662.Injection speed has great influences on the microstructure and mechanical properties of semi-solid AlSi9Mg alloy. In this experiment, suitable injection speed is 1.5~2.0m/s. When injection speed is 1.5m/s, the tensile strength of the sample is 238MPa, elongation percentage is 5.7%, Brinell hardness is 83, and impact toughness is 134kJ?m-2. In microstructure the primary solid fraction is 38.9%, the average diameter of primary solid phase is 22.7μm, roundness is 0.663.At every transverse section of rheology die casting primary solidα-Al grains are nearly spherical, rather than ordinary die casting dendrite grains. Along alloy melt filling process the change of roundness in the microstructure is small, the difference does not exceed 0.1. Primary solid fraction has a wave-shaped change, and the value change is around 20%. The average diameter of grains is 10~25μm. It changes irregular. Solution treatment parameters have great influences on the microstructure and mechanical properties of rheology die casting. Solution treatment temperature has a significant impact on the tensile strength and elongation. In this experiment, the suitable solution treatment process for rheology die casting is that the solution heat treatment temperature is 535℃, holding time is 2h, water temperature is 80℃. Under this solution treatment parameters tensile strength of the sample is 305MPa, elongation percentage is 15.3%, Brinell hardness is 107.