Microstructure characteristics and liquation behavior of fiber laser welded joints of Mg-5Zn-1Mn-0.6Sn alloy sheets

Fine-grained Mg-5Zn-1Mn-0.6Sn alloy sheets of 2 mm in thickness were welded by fiber laser welding. The appearance and microstructures of the welding joints and liquation behaviors in the partially melted zone (PMZ) were investigated. The results show that, with the lower welding power and higher welding speed, the width and depth of the joints decrease. Moreover, some pores are detected at a very high welding speed. There are two kinds of liquation phenomena in the PMZ. One is the liquation network along grain boundaries associated with the liquation of substrate and segregation-induced liquation, the other is the molten pool involved with the liquation of the residual second phases at the boundaries. However, the liquation of substrate and the segregation-induced liquation are the main liquation mechanism in the PMZ.