Papers by Author: Zong Yi Ma

Abstract: 5 mm thick 2014Al-T6 alloy plates were friction stir welded at the welding speeds of 100-400 mm/min and the rotation rates of 400-800 rpm. The influence of post weld artificial aging and T6 treatments on the microstructure and mechanical properties of FSW 2014Al-T6 joints were investigated. It was found that artificial aging did not alter the grain structure but T6 heat treatment caused the abnormal grain growth at the nugget zone. The tensile strength of the joints could not be enhanced by the artificial aging treatment but were improved by the T6 treatment. The effectiveness of T6 treatment is related with the distribution of “S” line.

Abstract: In this article, recent investigations on magnesium alloys by friction stir processing (FSP) are addressed. It indicates that remarkable grain refinement and breakup/dissolution of second-phase particles could be achieved simultaneously by FSP. High values of superplastic elongation were achieved in the FSP magnesium alloys at a wide range of strain rates and temperatures. The pinning of heat resistant particles on the grain boundaries in Mg-RE alloys stabilized the fine microstructure, leading to the occurrence of superplasticity at higher temperature and higher strain rate.

Abstract: The present investigation is aimed at evaluating the influence of tool rotation rate and welding speed on the microstructure, tensile properties, and fracture mode of 6061 Al-T651 alloy after friction stir welding (FSW). TEM results revealed that in the nugget zone (NZ), FSW resulted in the dissolution of fine needle-shaped precipitates that previously existed in the base metal. At a given rotation rate of 1400rpm, the yield strength (YS) and ultimate tensile strength (UTS) of the welded joints increased with increasing welding speed from 200 to 600mm/min. However, the UTS of the joints was nearly independent of the rotation rate. Furthermore, the relationship between the hardness distribution and fracture location has also been identified.