The effects of trace y on the microstructure and mechanical properties of Mg nd Zn Alloy by metal mold casting and rheo squeeze casting were studied. The composition of the alloy was optimized and the alloy with excellent properties was obtained. The main conclusions are as follows
(1) With the increase of Y content, the average grain size of as cast metal mold casting and rheo squeeze casting alloys decreases, and a small amount of mg24y5 phase is formed in the Y-containing alloy, which is uniformly distributed at the grain boundary of the alloy with 0.39 wt.% Y (0.12 at.% y) content.
(2) The number of acicular mg12nd phase in the grains of the alloy increases with the increase of Y content. After solution treatment, needle like mg12nd phase and mg24y5 phase almost completely dissolve into α – Mg matrix, forming long rod like zn2zr3 phase. However, the residual mg12nd phase can be detected at the grain boundary of Y-containing alloy. Based on the experimental data, a yield strength model was established to predict the yield strength of 0.39 wt.% y alloy.
(3) The aging strengthening effect of Mg – 0.43nd – XY – 0.08zn – 0.11zr alloy obtained by two different forming methods increases with the increase of Y content. After aging treatment, the number of long rod like zn2zr3 phase in the alloy with 0.39 wt.% y content increases significantly, and the number of this phase is more than that in the alloy without y due to the segregation of Zn atoms.
(4) Under all experimental conditions, the alloy with 0.39 wt.% y content has the best comprehensive mechanical properties, especially in the range of 200-300 ° C, the metal mold casting alloy has higher yield strength (about 150 MPa). The improvement of the mechanical properties of the alloy is mainly due to the joint effects of grain refinement, solid solution strengthening, zn2zr3 phase and β′ phase strengthening.
(5) Arrhenius model was established to describe the effect of deformation temperature and strain rate on flow stress of 0.39 wt.% y alloy in metal mold casting: σ = (169.69 𝜀̇𝑒𝑝 (223045 𝑅𝑇)) 0.098. The strain index and activation energy of the alloy are higher than those of the alloy without y element.
(6) Compared with the metal mold casting alloy, the grain size of the alloy with 0.39 wt.% y content is refined and the mechanical properties of the alloy are further improved. After T6 treatment, the yield strength, tensile strength and elongation of the alloy can reach 168 MPa, 329 MPa and 8.7% respectively.