Structure, fluidity and mechanical property of semi-solid AZ91D magnesium alloy fabricated by pressure casting

Abstract

An AZ91D magnesium alloy was reheated to the temperature of the semi-solid state and was pressure-cast by employing a die casting machine. The effects of casting conditions on structures, fluidity and mechanical properties were investigated. Fluidity is improved by using stir-cast materials and by increasing both the reheating temperature from 570°C to 580°C and the plunger speed from 0.6m/s to 1.1m/s. The improved fluidity results in the uniform flow of the solid and liquid and produces sound products without any macroscopic defects caused by the entrapping gas bubble. But low temperatures of the permanent mold and the temperature drop of the semi-solid materials in shot sleeve lead to form microscopic defects. Tensile strength of the specimen with good fluidity is 140-200N/mm² and is higher than that of an as-stirred specimen, but is lower than that of a die-cast specimen.