Huashun Yu

Microstructure and Tensile Properties of ZK60 Alloy Fabricated by Simplified Rapid Solidification Powder Metallurgy (S-RS P/M) Process

This study investigated the microstructures and mechanical properties of ZK60 alloy prepared by a simplified rapid solidification powder metallurgy (RS P/M) processing system (S-RS P/M), which consists of warm press in dry air and hot extrusion. Microstructure characterizations showed that S-RS P/M alloy consisted of magnesium matrix and oxide stringers of ∼1 μm in width. TEM (transmission electron microscopy) observations illustrated nano-size magnesia particles (10–30 nm) constituted oxide stringer in detail. Due to a relatively higher volume of nano-size magnesia particle produced during S-RS P/M process, 0.2% yield strength of S-RS P/M ZK60 alloy was found to be as high as 382 MPa, which is 10% higher than that of RS P/M alloy. The improvement in mechanical properties is mainly attributed to the combination effects of Orowan mechanism and coefficient of thermal expansion (CTE) mismatch because of the approximately same average grain size.

Electron Backscattered Diffraction Analysis of Eutectic Solidification in a Continuous Cast Aluminum Alloy Billet

Eutectic silicon structure was modified by fine-grained structural material as the master alloy. An investigation of the crystallographic orientations of eutectic colonies has been carried out by electron backscatter diffraction. The morphologies of eutectic silicon alter from lamellar to fibrous shape after adding 30% fine-grained structural material master alloy. The coupling relationship of eutectic colonies becomes stronger in modified aluminum–silicon alloys. Furthermore, the misorientation angles in the eutectic colony change from high angle grain boundaries (≥15°) to low angle grain boundaries (≤5°). The misorientation angles inside eutectic silicon decrease from 60° to low angle grain boundaries (≤5°). The primary α-aluminum dendrite and neighboring eutectic aluminum have almost the same crystallographic orientation in modified aluminum–silicon alloys.