Study On Microstructiue And Properties Of Selective Laser Melting Magnesium-Aluminum Alloy

Magnesium alloy is a very promising alloy material,which has good shock absorption ability and electromagnetic shielding.And magnesium alloys are of great help in reducing weight in cars and aircraft because of its high specific strength and specific stiffness.Selective laser melting(SLM)technology can manufacture parts by near-net-shape forming,which greatly improves production efficiency,and the rapid solidification method of SLM technology can improve the microstructure of magnesium alloys,which promote the development and application of high-performance magnesium alloys.In this experiment,Mg-Al-Zn,Mg-Al-Zn-La,and Mg-Al-Zn-Cu alloy samples were prepared by SLM technology,and each sample was heat-treated in different ways using a vacuum furnace.The microstructure,phase composition,hardness and micromechanical properties of the prepared magnesium alloy samples were observed and measured by means of optical microscopy,XRD,SEM,EDS,microhardness,nanoindentation,and micro-scratch.The effects of laser power,element addition amount and heat treatment method on the microstructure and properties of SLM magnesium alloy were studied.The results show that the laser power has a great effect on the surface morphology and micromechanical properties of Mg-Al-Zn alloy.At 80 W,the relative density of the sample reached 99.2%.With the increase of laser power,the temperature of the molten pool increased and vaporization intensified,which leaded to the decrease of relative density.The grain size of the sample is between 1.3 ?m and 2.0 ?m,and the grain size is the smallest at 105 W.The linear relationship between the microhardness of the sample and the solid solubility of the solid solution atoms was obtained by fitting calculation(?2.72 kg·mm-2/at%).After solution treatment,the hardness and abrasion resistance of the sample were reduced.After the solution treatment and aging treatment,a short rod-shaped Mg17Al12 phase was formed.The microhardness increased to 129 HV,and the friction performance was also improved.For Mg-Al-Zn-La alloys,different amounts of La2O3 were added for comparison tests.When the nominal La content increases from 0%to 2%,the microstructure changes from a continuous network?discontinuity? continuous? network dendrite thickening trend,and the amount of rare earth phase Al11La3 also increases.The coefficient of friction decreases slightly with the addition of La,but it is not sensitive to the heat treatment under the same La content.Nano-hardness value of Mg-6Al-1Zn-0.5La after solution+aging treatment reaches 1903 MPa,elastic modulus is 61.0 GPa,the rebound rate of indentation is 86.9%,and the microhardness of Mg-6Al-1Zn-2La alloy after solution and aging treatment reaches maximum 140 HV.Under the load of 100 mN,the absolute value of the residual depth is reduced from 361 nm(unheated sample)to 127 nm,and the friction performance optimization effect is significant.For Mg-Al-Zn-Cu alloys,different amounts of Cu were also added for comparison tests.When the Cu content increases from 0%to 2%,the grain size tends to decrease continuously.However,when the Cu content was increased from 2%to 4%,the grain refining effect was weakened,resulting in a significant increase in grain size and coarse dendrites between grain boundaries.Under the load of 100 mN,compared with 0%Cu sample,the absolute value of the residual depth of the 2%Cu sample was reduced from 580 nm to 311 nm,and the friction coefficient was reduced from 0.21 to 0.14,so Mg-6Al-1Zn-2Cu alloy has the best wear resistance and antifriction.After the solution+aging treatment of Mg-6Al-1Zn-2Cu alloy,the maximum microhardness is 137 HV,the nano-hardness is 2045 MPa,the elastic modulus is 37.9 GPa,and the indentation rebound rate is 80.6%.