Effect of Heat Treatment and Rolling Process on Microstructure and Deformation Behavior in Al-Si Alloy

Recently, high strength at high temperature can be achieved by inducing kink bands in alloys having aligned lamellar microstructure. However, the kink-bands formation has been confirmed only in alloys with lamellar microstructures, where slip plane is limited to the plane parallel to the lamellar interface, and not confirmed in alloys with rod-like or Chinese script microstructures. In this study, we clarified the contribution of rod-like Si phases in Al-Si alloy on the mechanical properties and focused on the feasibility of introduction of kink bands in the alloys without lamellar structure. The results showed that in Al-Si eutectic alloys, the non-lamellar second phase, i.e., the Si phase, is aligned by directional solidification, and refined by rolling. The directionally-solidified sample showed high yield strength with long and aligned Si phase, while the rolled samples showed high ductility with refined microstructure. The rolled samples were uniformly deformed in all the samples with variety of reduction ratios, and wedge-shaped deformation bands were observed after the compression test, especially in the 5-10% rolled specimens. Crystallographic orientation analysis indicated that these deformation bands were not kink bands but were localized slip bands.