Twinning Behavior in Magnesium Alloys Processed by Laser Shock Peening

Mg and its alloys are very promising structural materials due to their high strength-weight ratio, good recyclability and desirable bio-compatibility. However, use of Mg alloys is often restricted by their poor mechanical properties. Recent studies indicate that a novel laser-based surface processing technology, laser shock peening (LSP), is promising to improve the engineering performance of Mg alloys by enhancing their surface strength, biocompatibility, fatigue resistance, and anti-corrosion ability. Despite these experimental efforts, little attention has been paid to study the surface microstructure evolution in the LSP process, particularly the formation of high density deformation twins. Deformation twinning in hexagonal closed-packed (HCP) crystal structure plays a fundamental role in enhancing mechanical performance of Mg alloys. This research is to establish the process-microstructure relationship of Mg alloys as processed by LSP. A focus is placed on understanding the deformation twinning mechanism. LSP experiments are conducted on a rolled AZ31B Mg alloy. The microstructures before and after laser processing are characterized. The effect of laser intensity on the twin volume fraction is investigated. Twin-twin interactions during LSP process are characterized and analyzed. The twinning induced surface hardening effect in LSP is investigated.