Microstructure And Properties Of CA Cladding Aluminum Composite Layer On AZ61 Magnesium Alloy

Magnesium alloy is a lightweight structural material with low density,high specific strength,high electrical and thermal conductivity.It is widely used in aerospace,automotive,biological,electronic and electrical fields.However,the poor hardness,wear resistance,and corrosion resistance of magnesium alloys have severely limited their advantages in industrial applications.Many physical or chemical methods have been applied to the surface modification of magnesium alloys at the present time.However,there are still some problems with these surface modification technologies,such as high cost,thin coating and complicated process.Arc cladding is a mature low-cost and high-efficiency surface modification technology,and using this technology to improve the surface properties of magnesium alloys is significance for expanding the application range of magnesium alloys.In this paper,three kinds of cladding wires,Al-Mn alloy?AlMn1?,Al-Si alloy?AlSi5?and Al-Mg alloy?AlMg5?,were cladded on the surface of AZ61 magnesium alloy by pulsed direct current?P-DC?cold arc?CA?for a comparative study.This will provide theoretical reference and practical experience for the CA cladding process on magnesium alloys.The microstructure and phase composition of the coatings were carefully studied by optical microscopy,scanning electron microscope?SEM?,energy dispersive spectrometer?EDS?and X-ray diffractometer?XRD?.The hardness,wear and corrosion resistance of the cladding layers were measured by microhardness tester,friction and wear tester,and electrochemical workstation,espectively.The experimental results show that the defects?such as pores,cracks,etc.?of the cladding layers decrease as the heat input decreases.And different heat input causes the cladding layer to have different geometric parameters,which can be divided into a stable forming interval and an unstable forming interval.The acceptable heat input intervals for depositing Al-Mn,Al-Si and Al-Mg alloy cladding layers are 260-310J/cm,290-330J/cm and 220-255J/cm,respectively.The cladding layers are mainly composed of?-Al solid solution,Al₃Mg₂ and Mg₂Si.Intermetallic compounds?IMCs?are continuously distributed in the transition zone,and sequentially form Al₃Mg₂ sub-layer,Al₁₂Mg₁₇ sub-layer and Mg+Al₁₂Mg₁₇ eutectic sub-layer.As the heat input decreases,the thickness of the transition layer and the Al₃Mg₂ sub-layer becomes thinner,while the thickness of the Al₁₂Mg₁₇ sub-layer and Mg+Al₁₂Mg₁₇ eutectic sub-layer is basically unchanged.Inner the Al-Mn cladding layer,the macrosegregation composed of Al₃Mg₂+Al₁₂Mg₁₇7 eutectoid structure was formed by insufficient mixing of the molten pool.The cladding parameters have an influence on the formation of macrosegregation,and the sensitivity of segregation decreases with the decrease of heat input.In the interlayer of the Al-Mg alloy cladding layer,surfing flow of the melted base metal caused a macrosegregation zone composed of?-Al and Al₃Mg₂.Compared with the AZ61 magnesium matrix,the hardness of the three aluminum composite layers are significantly improved.The microhardness of the three aluminum alloy single-clad samples is 70.3-133.1HV higher than that of the AZ61 matrix.The reduction of the dilution rate leads to a reduction in the hardness of the multi-lap cladding layer,which is 3 times,2 times and 1.4 times of the substrate,respectively.The Al-Si and Al-Mg alloy cladding layer effectively improves the wear resistance of the AZ61 substrate.The improvement in wear resistance is the result of the combined effect of the reinforcement phase and the Al matrix,and excessive IMCs?Al₃Mg₂?content led to the deterioration of the wear resistance of the Al-Mn alloy cladding layer.Compared with the substrate,the self-corrosion voltage of the three aluminum composite layers is increased by 0.23-0.43V,and the self-corrosion current density is 1-2 orders of magnitude lower than that of the AZ61 substrate.The corrosion resistance decreases in the order of Al-Mg alloy cladding layer,Al-Si alloy cladding layer,Al-Mn alloy cladding layer and AZ61 substrate,and the EIS test results are consistent with the results of the potentiodynamic anodic polarization curves recorded.The experimental results show that the CA cladding process can be used to prepare well-bonded Al-Mn,Al-Si and Al-Mg alloy cladding layers on the surface of AZ61 substrate.And reducing the heat input helps to reduce defects and improve the connection strength between the cladding layer and the substrate.