Research On Forming,microstructure And Mechanical Properties Of Magnesium Alloy Component Deposited By AC-TIG Robotic Weaving Arc Additive Manufacturing Process

As the problems of inconsistent layer height and uneven pass width of multi-layer and multi-pass additive component in medium-thickness AZ31B magnesium alloy deposited by wire arc additive manufacturing process,based on the alternating current-tungsten inert gas arc additive manufacturing process,the relationship between weaving parameters and magnesium alloy additive component forming was studied.This paper used the response surface method to design quadratic regression universal rotating combination experiment programs,and conducted the experimental research on the single-pass forming and multi-pass forming of magnesium alloy,in order to obtain the control principle of magnesium alloy additive component forming and provide support for the choice of weaving parameters.Firstly,the relationship between the weaving parameters and the magnesium alloy single-pass additive forming was studied,and five regression models between the weaving parameters and the single-pass forming sizes were established.Through response surface method,it was found that within the weaving parameters window,the interaction between weaving amplitude and weaving frequency（W_d×f）and the interaction between weaving amplitude and travel speed(W_d×v_w)have a significant effect on the single-pass forming size.W_d×f can synergistically promote the increase of the welding width and its unit change.When W_d=4.68mm and f=3.34Hz,the welding width reaches 22.91mm.When weaving frequency f<2.5Hz,the welding penetration decreases with the increase of W_d.When f>2.5Hz,the layer height and wetting angle decrease with the increase of W_d.W_d×v_w has a significant effect on the welding penetration and trough height.The maximum value and maximum variation of the welding penetration and trough height are obtained when W_d=1.32mm and v_w=13.18cm/min.Based on the regression models,the optimized weaving parameters of magnesium alloy single-pass forming are:weaving amplitude 2.98mm,weaving frequency 2.15Hz,residence time 0.35s and travel speed30.19cm/min.Secondly,the relationship between the process parameters and the forming characteristic parameters of the magnesium alloy multi-pass additive layer was studied,and three regression models between the process parameters and the multi-pass forming characteristic parameters were established.The response surface method analysis results show that the surface flatness first increases and then decreases under the influence of each interaction,and the maximum value are obtained in the zero level area.When the offset d>11mm,select W_d<3mm or residence time t_w<0.3s or v_w>30cm/min can reduce the average height difference of the wave crests.The average height of the wave crests takes the maximum value of 4.70mm when t_w=0.5s and v_w=20cm/min.Using the established regression models,the optimized magnesium alloy multi-pass additive process parameters are:weaving amplitude 2.56mm,weaving frequency 2.5Hz,residence time 0.3s,travel speed 30cm/min and offset 11.46mm.Finally,the optimized multi-pass additive process parameters were used to deposit a magnesium alloy additive component.The microstructure of the additive component is distributed in layers,and the microstructure of the inter-layer zone are mainly composed of fine columnar dendrites and coarse columnar dendrites and coarse equiaxed crystals.The microstructure of the inter-pass zone includes long equiaxed crystals and coarse equiaxed crystals and fine columnar dendrites.The mechanical properties of the magnesium alloy component showed that the horizontal tensile properties are best,the tensile strength reaches241 MPa,and the elongation is increased by 86%compared with the standard level.The microhardness value in the horizontal direction changes periodically,and the microhardness value in the vertical direction fluctuates up and down in the range from 60HV to 100HV.