Microstructure and properties of AL-SI alloy cladding on AZ91D magnesium alloy by low heat input DC-PMIG welding

The corrosion resistance of magnesium is an important research field for useful application in industry. In order to form a corrosion resistant layer with enough thickness and strong adhesion on the surface of magnesium alloy, a low cost and efficient production process direct current (DC) pulse metal inert gas (PMIG) welding was used to deposit Al-Si alloy on AZ91D magnesium matrix. The heat input was strictly controlled to form compact metallurgical coating with a maximum thickness of 1.8 mm. The composite layer can be divided clearly into three zones: Mg matrix zone, the transition zone composed of a variety of intermetallic compounds (Al22Mg17, Al3Mg2 and Mg2Si etc.), and alloy coating (alpha-Al dendrites, Al-Si eutectic and Mg2Si.) zone. Furthermore, the properties of the alloy coating zone were investigated by both micro-hardness test and electrochemical corrosion. The micro-hardness of the coating is almost two times higher than that of the matrix and the corrosion resistance of the coating was greatly improved compared with that of the matrix.