The microstructure characteristics and mechanical properties of 7075 aluminum alloy produced by a new rheoforming technique,under as-cast and optimized heat treatment conditions,were investigated.The present rheoforming combined the innovatively developed rheocasting process,named as ICSPC(inverted coneshaped pouring channel)process,and the existing HPDC(high pressure die casting)process.The experimental results show that the ICSPC can be used to prepare high quality semi-solid slurry for the subsequent die casting.Compared with conventional HPDC process,the ICSPC process can improve the microstructures and mechanical properties of the cast tensile samples.An optimized heat treatment results in significant improvement in ultimate tensile strength.However,the ductility of the samples,both under as-cast and optimized heat treatment conditions,are relatively poor.
The further application of semi-solid processing lies in the in-depth fundamental study like rheological behavior. In this research, the apparent viscosity of the semi-solid slurry of 7075 alloy was measured using a Couette type viscometer. The effects of solid fraction and shearing rate on the apparent viscosity of this alloy were investigated under different processing conditions. It can be seen that the apparent viscosity increases with an increase in the solid fraction from 10% to 50%(temperature 620 oC to 630 oC) at steady state. When the solid fraction was fi xed, the apparent viscosity can be decreased by altering the shearing rate from 61.235 s-1 to 489.88 s-1 at steady state. An empirical equation that shows the effects of solid fraction and shearing rate on the apparent viscosity is fi tted:. The microstructure of quenched samples was examined to understand the alloy's rheological behavior.
