The effect of die temperature on the microstructure and mechanical properties of rheo squeeze casting nz30k alloy was studied. In the process of rheo squeeze casting, the alloy semi-solid slurry fills the mold cavity under pressure and solidifies at the same time. The pressure has great influence on the primary particles and residual liquid phase in semi-solid slurry. Therefore, the effect of pressure on the casting and mechanical properties of rheo squeeze casting nz30k alloy (mg-3.3nd-0.21zn-0.41zr) was studied.
At present, different scholars have studied the effect of pressure on rheo squeeze casting Mg alloy. The effect of pressure on Microstructure and mechanical properties of rheo squeeze casting mg-re-zn-y alloy was studied by Fang et al. The results show that with the increase of pressure, the primary α – Mg particles in the alloy structure are refined and rounded, the solid solubility of solute atoms in Mg matrix increases, and the second phase rich in rare earth is more and more evenly distributed at the grain boundary of primary particles. Therefore, the mechanical properties of as cast alloy increase with the increase of pressure. Zhang et al. Found that with the increase of pressure, the microstructure of rheo squeeze casting az91-2wt.% CA alloy was refined, the porosity decreased and the mechanical properties increased. The reason of grain refinement is that the increase of pressure increases the cooling rate of slurry and liquidus of alloy, which increases the undercooling and promotes the nucleation of melt.
Although different scholars have studied the effects of pressure on phase composition, grain size, alloy density and mechanical properties of rheo squeeze casting alloys, the effects of pressure on undercooling and nucleation rate of alloy melt are still unclear. Therefore, in this chapter, in addition to using conventional characterization and testing methods to study the effect of pressure on the microstructure and mechanical properties of nz30k alloy, we will also focus on the theoretical analysis of the relationship among pressure, undercooling and nucleation rate of nz30k alloy during rheo squeeze casting. In addition, the contribution of different strengthening factors to rheo squeeze casting, metal mold casting and conventional squeeze casting was compared and analyzed to clarify the strengthening mechanism of the alloy under the above three different forming methods.