The semi-solid slurry of nz30k alloy was squeeze cast under different pressures. The effect of pressure on Microstructure and mechanical properties of nz30k alloy was studied. In addition, nz30k alloy was prepared by metal mold casting and conventional squeeze casting. The strengthening mechanism of Mg nd Zn alloy obtained by different forming processes (metal mold casting, conventional squeeze casting and rheo squeeze casting) was discussed by comparing the microstructure and mechanical properties of the alloy formed by the above two forming methods. The main conclusions are as follows
(1) With the increase of pressure, the solid solubility and dislocation density of Nd and Zn in α – Mg increase. The mechanical properties of nz30k alloy first increase and then decrease with the increase of pressure. The increase of mechanical properties is mainly due to grain refinement and microstructure densification, and the decrease of mechanical properties is mainly due to the plastic deformation between primary particles and large stress concentration.
(2) The yield strength, tensile strength and elongation of T6 nz30k alloy can reach 165 MPa, 309 MPa and 5.7%, respectively.
(3) Based on Clausius Clapeyron equation, the mathematical expressions of pressure, undercooling and nucleation rate can be derived
It is found that the nucleation rate of nz30k alloy increases with the increase of pressure when the undercooling is less than 13.8 ℃. Under the experimental conditions, with the increase of pressure, the nucleation rate of alloy melt increases.
(4) Compared with the metal mold casting alloy and the conventional squeeze casting alloy, the grain size of rheo squeeze casting alloy is smaller, the eutectic structure is smaller and less, and it is evenly distributed among the particles, so the comprehensive mechanical properties of rheo squeeze casting alloy are higher.
(5) After T6 treatment, the precipitates in rheo squeeze casting nz30k alloy are β″ phase and β′ phase, while the precipitates in metal mold casting alloy and conventional squeeze casting alloy are mainly β′ phase. Due to the grain refinement effect, the mechanical properties of the alloy prepared by rheo squeeze casting are higher than those prepared by metal mold casting; due to the large precipitation strengthening effect, the mechanical properties of the alloy prepared by rheo squeeze casting are higher than those prepared by conventional squeeze casting.