Yuchun Yuan

Finite Element Analysis of the Deformation Distribution During Multi-Pass Rotary-Die ECAP

Rotary-die equal channel angular pressing (RD-ECAP) is a specially designed continuous processing technique to prepare bulk ultrafine-grained/nanostructure (UFG/NS) materials. In this article, an Al-7wt.% Si-0.35wt.% Mg alloy was processed by up to four RD-ECAP passes. The deformation behavior was studied by experiments and FEM simulation, including the observation of the scribed deformation patterns, the macrostructures, the simulated flow lines feature, and the equivalent stain distribution after different RD-ECAP passes. The results show that the shear deformation can accumulate effectively all over the entire billet via multi-pass RD-ECAP. The observed zigzag shape metal flow is formed after three ECAP passes, and the structure homogeneity can be achieved by RD-ECAP with more processing passes.

Corrosion behavior of hypereutectic Al-23%Si alloy (AC9A) processed by severe plastic deformation

Ultrafine-grained(UFG) hypereutectic Al-23%Si (mass fraction) alloy was achieved through equal-channel angular pressing(EACP) procedure. And the electrochemical properties after various ECAP passes were investigated in neutral NaCl solution. Potentiostatic polarization curves show that the corrosion potential of the ECAPed sample after 4 passes decreases markedly, while the corrosion current density reaches 1.37 times that of the as-cast alloy. However, the φcorr and Jcorr values after 16 passes are improved and approach those of the as-cast alloy. Immersion tests also show that the mass-loss ratio of ECAPed alloy decreases with increasing the pressing pass, which is lowered to 28.7% with the increase of pass number from 4 to 16. Pitting susceptibility of the ECAPed alloy after initial 4 passes is boosted, due to the presence of biggish voids resulted from the breakage of brittle large primary silicon crystals during ECAP. Increasing ECAP pass makes the voids evanesce and results in the homogeneous ultrafine-grained structure, contributing to a higher pitting resistance. These results indicate that enough ECAP passes are beneficial to increasing corrosion resistance of the hypereutectic Al-23%Si alloy.