This paper presents a comparative study of laser welding-brazing Mg to steel with four different coating surfaces, including (Znzpre-existing Fe-Al phase), pure Zn coating, pre-existing Fe-Al phase and fresh steel without any coating. The presence of Zn coating was found to significantly improve the wettability of liquid filler on steel. However, Mg-Zn products enriching at the seam head tended to cause cracking. The weak bonding of Mg-Zn products and Fe-Al layer was mainly responsible for the decreased tensile strength and interfacial failure that occurred in joints with the first two coatings. For joints with the latter two coatings, the thickness of newly formed Fe-Al layer determined the mechanical properties. The reaction layer formed at the Mg/fresh steel was thin, inducing interfacial failure, whereas the joint with pre-existing Fe-Al phase fractured at the seam, indicating that the pre-existing Fe-Al phase was beneficial to formation and growth of the Fe-Al phase.
In order to overcome the difficulties of laser melt injection (LMI) on aluminium alloys, the process of tungsten inert gas (TIG) arc enhanced LMI ceramic particles was developed. The influence of process parameters, including laser power, TIG current, the direction of powder feeding, the carrier gas flow of powder and the shield gas flow of TIG, was investigated. The results have shown that to achieve appropriate surface enhancement effect, the powder should be fed from the back side of the laser beam. The depth of the arc enhanced LMI layer increases monotonously with increasing TIG current. The depth of the LMI layer increases first and then decreases with increasing laser power. The carrier gas flow and gas flow of TIG should be matched. Through optimisation of process parameters, WCp/Al layer was prepared successfully on the surface of aluminium alloy. The microstructure of the surface layer prepared by arc enhanced LMI was analysed.
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