Microstructure Evolution Of Mg-1Sn-2.5Y Alloy Solidified Under High Pressure

In this paper, the effects of high pressure(1GPa and 1.5GPa) and cooling conditions on solidification structure were studied by using Mg-1Sn-2.5Y(wt%) alloy as the research object, including microstructure evolution and phase composition and the evolution mechanism are discussed. The research content is to enrich and develop the solidification theory, and to provide a scientific theoretical basis for the synthesis of new materials with high pressure technology.Research results show that the solidification pressures of 1GPa and 1.5GPa, high pressure cavity low cooling rate for 600K/min, high cooling rate for 900K/min solidification Mg-1Sn-2.5Y alloy, by the high speed cold end to low speed cold end grain size increases, the grain size number of levels by 2 fell to- 1. High cold speed end large temperature gradient, solidification area is very narrow, with by layer solidification formed fine equiaxed grains. Low cold speed end small temperature gradient, solidification area is wide, with volume solidification formation rules of thick dendrite, a branch arm is longer.Reduce the fine equiaxed grains leading edge cooling rate, temperature gradient and no optimal direction of heat dissipation, formation of equiaxial grain. Opposite ends of the growth, thick equiaxed grain frontier and thick rules dendritic close to each other, perpendicular to the line of best cooling direction formed columnar crystal. Line endpoint with the pressure increases near to low cooling speed end, the middle point of boundary basically unchanged.Research results show that the solidification pressures of 1.5GPa, high pressure cavity low cooling rate for 600K/min, high cooling rate for 1200K/min solidification Mg-1Sn-2.5Y alloy, by the high speed cold end to low speed cold end grain size increases, the grain size number of levels by 3 fell to- 1. High speed cold end to form a fine equiaxed grain, low cooling rate end to form a thick equiaxed, opposite ends of the growth, did not form a line. The high speed cold end cooling rate increases, the gradient of temperature increases, fine equiaxed grain area thickening and low speed cold end temperature gradient increases, thick equiaxed grains formed in the middle of the solidification mode.Atmospheric solidified Mg-1Sn-2.5Y alloy was composed of α-Mg matrix, a dispersed distribution of granular and elongated Mg Sn Y phase and a scattered distribution of large size rule block Mg Sn Y and a fish skeleton like、block Sn3Y5 phase.The coupling effect of high pressure and cooling conditions during solidification Mg-1Sn-2.5Y alloy form dendrite region of tissue from the α-Mg matrix and dendrite distribution of a skeleton type and block type Mg Sn Y phase composition, formation andcrystal axis tissue by α-Mg matrix、dispersed granular and strip shape Mg Sn Y phase composition and block Sn3Y5 phase.Mg-1Sn-2.5Y alloy α-Mg phase solute elements in ascending order: cast state <1GPa solidification dendrite region < 1.5GPa solidification dendrite region <atmospheric solid solution treatment state < 1GPa solidification equiaxed grain <1.5GPa solidification equiaxed grain. Dendrite region formed high pressure solidification Mg-1Sn-2.5Y alloy and α-Mg phase each diffraction peak phase compared with normal pressure were not happen offset; formation of equiaxed crystal zone, with the increase of the pressure, α-Mg phase each diffraction peak phase compared to atmospheric pressure to high angle offset increases.