Relationships between microhardness, microstructure, and grain orientation in laser-welded joints with different welding speeds for Ti6Al4V titanium alloy
(State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China)
Abstract: The microhardness curve trend and its relationships with microstructure and misorientation were analyzed to enhance the comprehension of the microstructure and mechanical property of micro-areas in Ti6Al4V laser-welded joints with different welding speeds. The microhardness measured on the fusion line (Hm) is the highest from the weld center to the base metal. Hm increases with increasing weld width in a welded joint and increasing degree of the non-uniformity in all studied welded joints. The microhardness decreases from the weld metal to the base metal with decreasing amount of martensite α'''' and increasing amount of original α phase. When the microstructure is mainly composed of martensite α'''', the microhardness changes with the cooling rate, grain size of the martensite, and peak values of the fraction of misorientation angle of the martensite in a wide weld metal zone or weld center at different welding speeds, whereas the difference is small in a narrow weld metal zone.
Key words: microhardness; microstructure; misorientation angle; non-uniformity; welding speed