Reseach On Technology And Performance Of Laser Deposition Repair Casting ZL114A Aluminium Alloy

Al-Si7-Mg(ZL114A)aluminum alloy belongs to casting Al-Si hypoeutectic alloy which has high strength.ZL114 A has been widely applied to structural component under high loads in automobile and aerospace industries because of its excellent casting performance and comprehensive mechanical properties.In this paper,based on the requirement of rapid repair of ZL114 A alloy parts after damage,the laser deposition repair process of penetrating crack and groove wear was studied.The comparisons between as-deposited specimen and Heat treatment state specimen in microstructure,micro-hardness,heat input and the properties were investigated.The main contents were as follows:The basic process experiment of multi parameter combination is accomplished by laser single-pass process,on the basic of analyzing surface features,the reasons of gas porosity,a set of optimized process parameters is obtained,and defect-free block specimens were prepared,microstructure analysis and mechanical property of the samples were carried out.The results showed that the repaired parts and the substrate formed a good metallurgical combination,at the bottom of the deposition layer were ?-Al columnar dendrites which approximately paralleled to the normal directions of the fusion line with epitaxial growth feature.The primary dendrite arm spacing is about 15.7 ?m,and the distance between secondary dendrites is about 5.27 ?m.Eutectic structure presented as bifurcated rod or block in shape,and continuously distributed in the gaps among dendrite crystals,and ?-Al columnar dendrites transformed into equiaxed crystal at the top of the last deposition layer.After the heat treatment,secondary dendrite arm of columnar dendrite is expansive because of atomic diffusion,and eutectic Si granulation were clear to be observed,the particle size is about 4.93 ?m,and part of them distributed uniformly on both sides of primary dendritic arm.The microhardness and room temperature tensile properties of the sample were tested.Due to the function of grain refinement and solution strengthening,the micro-hardness of the deposited area is 25.8% higher than that of the substrate.The hardness of repair area increased by an average of 55.5% than substrates after heat treatment,and the room temperature tensile properties were better than casting parts.The tensile strength at room temperature with repaired ratios at 10% and 20 %reach up to 90.4 % and 87.56% of the casting standard.The elongation was superior to the casting standard.The analysis of the fractography indicates that fracture mechanism of substrates is brittle fractured and that of the repair zone is ductile fracture.During the tensile process,in the substrate,the cracks initiated in the dense area of eutectic silicon partic and propagated along eutectic silicon particle,which was transgranular fracture.In repair zone,bypassing fine eutectic silicon particles,the cracks propagated along the combination area of Al-Si eutectic microstructure and dendritic cell,which was intergranular fracture.The parts with high repaired ratios(more than 30%)were conducted by the overall heat treatment after repair.After the overall heat treatment,the strength of repaired specimen was higher than that of casting.The result of thermopaint test heat input shows that if the maximum temperature was not exceeding 250?,the heat affected zone could satisfy the production requirements.The deformation test indicated that the deformation of repaired specimen could satisfy the production requirements.