Grain Refinement Of Wire Arc Additively Manufactured Al-Mg Alloy Based On In-Situ Alloying

Wire Arc additive manufacturing(WAAM)has the advantages of low equipment investment,high deposition efficiency,high material utilization and low operating costs.During the WAAM aluminum alloys,periodic heat input will result in the formation of coarse columnar grains and periodic cracks and other microstructures that affect the mechanical properties.Mechanical properties of perpendicular to the layer direction are lower than the along additive direction.Therefore,alloying elements are added during the WAAM process reacts in situ with the aluminum matrix to form a heterogeneous nucleation site,which promotes the columnar-equiaxed grain transformation and grain refinement,so as to improve mechanical properties of the WAAM aluminum alloys.First,forming regulation of single-layer single-bead,the effects of the interlayers waiting time and powder additional methods on the morphology and microstructure of thin wall components(TWCs)were studied.The results show that as the wire feeding speed increases and the additive speed decreases,the deposited metal has better spreadability,the forming height is reduced,the forming width is increased.TWCs sample has good forming morphology when the interlayer waiting time is 60s-150 s.Forming morphology and grain refining effect of the coating powder addition method better than powder feeder powder addition method.Then,the effect of in-situ alloying of different kinds of powders on the microstructure and mechanical properties of WAAM Al-Mg alloy was studied.Compared with un-added powder TWCs sample,after adding Ti powder,TiH powder and mixed powder(Ti: B4C=5:1),the Al3 Ti phase is formed.The grain shape of the interlayer changed from columnar grain to fine equiaxed grain,and layer center region is equiaxed grain.Grains of interlayer and layer center region is all significantly refined.The ultimate tensile strength(UTS)and elongation of added Ti powder TWCs sample increased by 21 MPa and 3.18% along the additive direction;26 MPa and 6.97% perpendicular to the layer direction.The difference in UTS between the two directions is reduced.UTS of the TiH and mixed powder samples were significantly reduced.Considering the improvement in microstructure and mechanical properties,the effect of in-situ alloying of Ti powder on the microstructure and mechanical properties of WAAM Al-Mg alloy was further studied.With the increase of Ti(0.115-0.328%),the columnar grain of interlayer in the added Ti powder TWCs sample was transformed into equiaxed grain.The grain size of the interlayer and layer center region is significantly reduced.When Ti content is 0.115%-0.136%,the UTS along additive direction increases 4-7MPa,and the elongation decreases slightly.The UTS and elongation increased significantly perpendicular to the layer direction.When Ti content is between 0.115% and 0.26%,the microstructure of TWCs samples is obviously improved.The UTS along the additive direction is slightly increased.Elongation is slightly reduced.The UTS and elongation perpendicular to layer direction has been greatly increased.Tensile properties in the two directions are more balanced.