Fabrication And Microstructure As Well As Properties Of Laserselective Melted Al-Mg-Zr Alloy

Selective Laser Melting(SLM)is an important technology for the preparation of high strength aluminum alloy.However,the types of aluminum alloy suitable for SLM forming technology are limited at present.Al-Si alloy is mainly applied in commercial aluminum alloy,such as Al Si10Mg,but neither the strength nor the elongation are satisfactory.Some aluminum alloys modified by rare earth Sc can obtain high strength and elongation,but expensive Sc hinders its large-scale application.The strength of an Al-Mg-Zr alloyspecially designated for SLM is similar to that of Al-Si alloy(<400 MPa),and its elongation(>20%)is high,but the improvement of its strength needs to be further explored.Based on SLM technology,a new medium and high strength lightweight Al-7.08Mg-0.48Zr-1.26Si-0.44Mn Alloy was designed and produced.Meanwhile,Al-3.54Mg-0.39Zr alloy was produced for mechanical properties comparison analysis.The main research contents and conclusions are as follows:Firstly,the influence of scanning speed and scanning spacing on the forming quality of Al-3.54Mg-0.39Zr alloy and Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy was studied to obtain the appropriate SLM process parameter interval.While other SLM process parameters remain unchanged,the actual densities of both Al-3.54Mg-0.39Zr alloy and Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy show a decreasing trend with the increase of scanning speed.At low scanning speed,the effect of scanning spacing on forming quality is not obvious.The process window suitable for Al-3.54Mg-0.39Zr alloy and Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy is:laser power 160 W,scanning speed 200?400 mm/s,scanning spacing 40?60?m,layer thickness 40?m.Secondly,the samples of Al-3.54Mg-0.39Zr alloy and Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy are formed under appropriate SLM process parameters,and the phase structure,metallographic morphology and mechanical properties of the Alloy in the deposited state are compared and investigated.The stacking morphology of molten pool in Al-3.54Mg-0.39Zr alloy and Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy is observed under an optical microscope,and cracks appear in Al-3.54Mg-0.39Zr alloy.It is observed in the XRD pattern that Mg₂Si phase is formed in Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy.The variety and quality of alloying elements in Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy increased respectively,thus forming more strengthening phases.Therefore,the?-Al diffraction peak in Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy shows an obvious deviation compared with that in Al-3.54Mg-0.39Zr alloy.After further alloying,due to precipitation strengthening and solid solution strengthening,both the tensile strength and the yield strength of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy are about 100%higher than that of Al-3.54Mg-0.39Zr alloy,and the elongation is about 44%higher.The SLM printed Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy can achieve a tensile strength of 428 MPa,yield strength of 285 MPa and an elongation of 11.5%.Finally,the micro-morphology of the Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy after aging is studied,and the phase structure,mechanical properties and fracture morphology of the Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy before and after aging treatment are analyzed.According to the observation under SEM,the microstructure of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy is composed of coarse equiaxed grain zone at the remelting pool boundary,fine equiaxed grain zone at the remelting pool boundary and columnar dendritic grain zone in the molten pool.Aging treatment eliminates the hardness orientation of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy,and the micro-hardness of X-Y and Z-direction of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy tends to be identical after aging treatment at 375?for 6 h.After aging at375?for 6 h,both the tensile strength and yield strength of Al-7.08Mg-0.48Zr-1.2Si-0.44Mn alloy are increased by 4.8%and 9.8%,respectively.The tensile strength and yield strength of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy are 448 MPa and 313 MPa,respectively,and the elongation is 11.0%.After aging at 325?for 6h,the strength and elongation of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy shows no significant difference from that of the deposited state.In other words,the aging temperature of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy should be higher than325?with the aging time 6 h unchanged.The tensile fracture of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy in both the deposition and aging state presents dimple fracture mode.Similar hard point particles are found in the tensile fracture of Al-7.08Mg-0.48Zr-1.26Si-0.44Mn alloy after aging at 375?for 6 h,and the precipitated hard phase prevents the plastic deformation of the Alloy,which functions as an important factor on the improvement of the Alloy strength.