The role of microstructure on the super plastic behavior

Abstract

In this work microstructure evolution and super plastic properties ofAZ31B Mg alloy processed by four routes in differential speed rolling with different speed ratio and reduction were studied in order to improve the poor plasticity of AZ31B alloy. In route UD, the sheet direction was kept constant and un changed between  repeated rolling passes ;while the sheet was  rotated  180^o about the rolling direction between repeated passes in route RD ;in ND route  the sheet was rotated through 180^o about the normal direction to the repeated passes ; In HY route the sheet was rotated 180^o about the rolling direction first and then rotated 90^o about the normal direction between repeated rolling passes .The results of microstructure observation showed that the modification of the microstructure had been affected by applied rout, rolling speed ratio and reduction. At low speed heavily twin structure appeared, as reduction percentage increase dynamical re-crystallization on the twins and shear bands were encouraged.  On the other hand increasing speed ratio caused an increase in the amount of dynamical re-crystallized grains and refined the microstructure. Ultrafine grains structure had been developed when the alloy was rolled by applying HY route at speed ratio of (1: 1.8) and 25% reduction, super plastic properties of rolled Samples were tested in tension at 673K and at initial strain rate ranging from1×10⁻³ s⁻¹to 2.2×10⁻³ s⁻¹.

Keyword: severe plastic deformation, Magnesium alloy, AZ31B, Super plasticity