Investigation On Microstructure Distribution And Properties Of ZL114A Aluminium Alloy Welded By Laser-arc Hybrid Welding

8mm thick ZL114A aluminium alloy has been single-pass welded by laser-arc hybrid heat source in this paper. The macroscopical morphology, composition and dimensional changes of the microstructure of the joints were mainly studied. We also analyzed the length and distribution ofα-Al dendrites in thickness and transverse directions, as well as changes of distribution microstructure gradient of the joints. The tensile strength of the whole specimen and slices, micro-hardness in the joint were investigated. This paper also discussed the relationship of the tensile strength withα-Al dendritic length and the microstructure gradient along the thickness direction.The research has discovered that both 4047 and 5356 mainly resulted in dendrites microstructures of alpha Al phase and the black (Al + Si) eutectic phase in the fusion zone. Length ofα-Al dendrites gradually decreases along the thickness direction of weld seam from top to root. This is called longitudinal microstructure gradient. In the joints welded with 4047 filler wire,α-Al shows significant dendritic growth morphology and a longer size. The transverse microstructure gradient is obvious. In the joints with 5356 wires, the higher Mg content results in second phase particles Mg2Si, which is beneficial for nucleation and refining of the size ofα-Al dendrites. This makes the transverse microstructure gradient smaller.Tensile strength of the whole specimen and slices in the thick plate joints obtained by single-pass welded with different Mg content wires,4047 and 5356, has been measured. The results show that the tensile strength of the slices decreases with the increase of the dendritic length. Tensile strength of the whole specimen decreases with the rise of the longitudinal microstructure gradient; the smaller the microstructure gradient is, the more uniformity it will be, the better coordination and properties of the whole joint will be. When the length ofα-Al dendrites decreases to 40μm, the tensile strength of the slices is 286MPa, which attains the tensile strength of base material after T6 treatment. The morphologies of the fracture surface show brittle transgranular fracture. There are lots of tear ridges and the quasi-cleavage plane on the fracture surface.The micro-hardness both in longitudinal and transverse directions of the joints welded by different wires has been measured. Longitudinal micro-hardness is roughly constant within a small range for different specimens. The longitudinal micro-hardness of joints obtained by single-pass welded with 5356 wires is higher than 4047 samples. The transverse micro-hardness distribution of hybrid welding joints experience a first decrease then rising process from the base metal to fusion zone. The micro-hardness at the base metal scatters, while it is relatively stable with a median in the fusion zone. The lowest micro-hardness appears in heat affected zone (HAZ), which is called softening area.