目的 在镁合金上堆焊Al-Si合金涂层，分析Mg/Al界面处过渡区的组织、成分与形成过程。方法 采用低成本、高效的直流脉冲熔化极气体保护焊（DC-PMIG welding），在低热输入下将ER4043（AlSi5）焊丝堆焊到AZ91D镁合金表面，形成Al-Si合金涂层。采用金相显微镜、扫描电镜、能谱仪、X射线衍射仪分析Mg/Al过渡区的微观组织，讨论过渡区的组织、成分，并分析其形成过程与机理。结果 过渡区分为两部分。区域I的主要成分依次为Mg+Al12Mg17、Al12Mg17、Al12Mg17+Al3Mg2和Al3Mg2，不规则块状Mg2Si相弥散分布于其中。区域II的主要成分为柱状α-Al，表面析出了大量点状Al3Mg2，α-Al柱状晶晶界处存在黑色点状Mg2Si。结论 直流脉冲熔化极气体保护焊能够在AZ91D镁合金表面制备Al-Si合金涂层，基体与涂层之间存在过渡区，过渡区中不同位置的镁、铝相对含量不同，成分也不相同。区域I与区域II中Mg2Si不同的析出顺序，使其微观结构不同：Mg2Si在镁含量相对较多的区域I中优先析出并长大，形成块状Mg2Si；而区域II中率先析出α-Al，随后在α-Al晶界处形成了黑色点状Mg2Si。

The work aims to overlayAl-Si alloy coating on magnesium alloy, and analyze microstructure, composition and formation process of the transition zone on Al/Mg interface. A low-cost high-efficiency production process-direct current (DC) pulse metal inert gas (PMIG) shielded welding was used to deposit Al-Si alloy coating on AZ91D magnesium alloy using ER4043 wires (AlSi5). Microstructure, morphology and composition of the Mg/Al transition zone were measured with metallurgical microscope, scanning electron microscope, energy-dispersive spectrometer (EDS) and X-ray diffractometer(XRD). Formation process and composition of the transition zone were analyzedas well. The transition zone consisted of two regions. Region I was made up of Mg+Al12Mg17, Al12Mg17, Al12Mg17+Al3Mg2 and Al3Mg2, respectively. Irregular massive Mg2Si phase was dispersed in region I. The region II was mainly made up of columnar α-Al, with plenty of precipitated dotted Al3Mg2, and there was black dotted Mg2Si on grain boundary of columnar α-Al. Direct current pulse metal inert gas shielded welding can be used to prepare Al-Si coating on AZ91D magnesium alloy. There is a transition zone between substrate and coating. Relative Mg and Al content and composition are differentin positions of the transition zone.The precipitation of Mg2Si in region I and region II was different, which explained the different morphology. Mg2Si preferentially precipitated and grew tomassive Mg2Si in region I with relatively high magnesium content, while α-Al precipitated first in region II, and subsequently forms black dotted Mg2Si on grain boundary of α-Al.