Study On Microstructure And Properties Of Laser Clad Layers In An A380 Aluminum Alloy

Aluminum and aluminum alloys have low density,high strength to weight ratio,good ductility,thus can be widely used in aerospace,automotive and portable electric devices.However,the disadvantages of Al and Al alloys include low hardness,poor wear and corrosion resistance,poor thermal stability,which limit the further applications.In order to extend the application field of aluminum and aluminum alloys,properties of aluminum alloy must be improved.In the present work,an A380 aluminum alloy was selected as the substrate material to be modified by laser surface treatment technology(including laser surface remelting and laser cladding).The microstructure,composition,hardness and corrosion resistance of the modified surface layer and the material before laser treatment were carefully investigated.The following conclusions are obtained:(1)After laser remelting treatment on A380 aluminum alloy,the sample cross section can be divided into three different regions,which are the melting zone in the upper part of the top layer,the transition zone at the bottom of the remelting layer and the matrix.The remelting layer mainly includes Al-Si eutectic,primary silicon and a small amount of Al-Si hypereutectic,Al and Al-Fe compounds.The surface microstructure of the remelting layer is obviously refined,and the average microhardness is increased by more than 35%compared to the substrate.After remelting,the impedance value in the 3.5wt%NaCl water solution becomes larger;the capacitance arc diameter increases;the corrosion potential increases and the current density decreases.The results indicate that the corrosion resistance of A380 aluminum alloy surface is greatly improved after laser remelting.(2)The Al/Ni/TiC powder with the mass ratio of 3:1:0.5 was laser clad onto the A380aluminum alloy surface.The clad layer with good adhesion to the substrate is obtained.The clad layer is mainly composed of TiC,Al,Al₃Ti,Al₃Ni and Al₄C₃.The average hardness of the sample is 163.8HV under the laser power of 3500W and the scanning speed of 2mm/s.The average hardness of the sample is 173.3HV under the parameters of laser power 3500W and scanning speed 4mm/s,which is 2.8².9 times higher than that of the matrix(⁵9.1HV).The corrosion potential of laser clad layer(about-1.2V)is lower than that of the substrate corrosion potential(-0.7170V),and the corrosion current density is higher than that of the matrix.Based on the analysis of polarization curves and EIS spectra,the corrosion resistance of clad layers decreases as compared to the untreated sample.(3)The Al/Ni/SiC powder with the mass ratio of 3:1:0.5 was laser clad on the surface of A380 aluminum alloy.XRD and EDS analysis showed that the cladding layer is mainly composed of AlNi compounds,Al-Si hypereutecti,primary Al and Al₄C₃.The upper part of the clad layer contains needle shaped grooves,which was probably trace of the primary Si formed from melt but is falling off in the process of the etching treatment.The average microhardness of the clad layer is 95±2HV,which is 65%higher than that of the matrix.The corrosion potential of the clad layer is about-0.8V at the scanning speed of 1mm/s,the laser power of 4500W and 4700W.The corrosion potential of the coating is-1.0359V at the scanning speed of 0.5mm/s and the laser power of 4700W.The corrosion potential of the clad layer was significantly higher than that of the substrate(-0.7180V),and the corrosion current density increased,which showed that the corrosion resistance of the cladding layer was decreased as compared to the substrate.(4)By comparing the 3 laser treatment methods,it is found that the hardness of the material can be significantly improved by laser cladding,while the laser remelting can improve the corrosion resistance of the surface.The corrosion resistance of the substrate was reduced due to the formation of the clad layer.A comparison of the two different powders cladding methods showed that TiC containing clad layer had a higher hardness than SiC containing clad layer due to the existence of unmelted TiC particles in the clad layer.Due to the high laser power,the majority of SiC particles are melted,and the hardness of the middle and bottom clad layer is much closer to the hardness of remelting layer.Based on the corrosion tests,although the corrosion resistance of the two clad layers decreased,the corrosion resistance of the clad layer added with SiC particles was slightly better than that of the clad layer added with TiC particles.