Microstructure And Properties Of Al-si-mg Alloys Formed By Laser Additive Manufacturing

Laser additive manufacturing(LAM)is an advanced forming technology,which is based on three-dimensional design model to directly fabricate alloy parts,by solidifying powder materials layer by layer with high-energy laser.It has been widely used now,due to its advantages of high material utilization,short manufacturing cycle,high process flexibility,and no restriction on processing methods or shape of parts.And because of the excellent physical and chemical properties such as high specific strength and high thermal conductivity,aluminum alloys have become a worldwide research hotspot.However,there are still problems such as poor surface quality in LAM of aluminum alloys.At the same time,its mechanical properties and corrosion resistance also need to be further improved.Therefore,develop new aluminum alloy materials that suitable for laser additive manufacturing is of great significance.In this paper,Y and Nb were used as alloying elements in hypoeutectic Al Si10 Mg alloy powder.Designed compositions of alloys and fabricated samples by LAM.To understand alloys’ microstructures and properties,systematically analyze effects of Y,Nb and their contents on microstructure and properties.Microstructure,formability,mechanical properties,wear resistance and corrosion resistance were tested by SEM,XRD,micro-hardness tester,etc.Experimental results showed that LAM Al Si10 Mg alloy was composed of primary α-Al dendrites and(Al+Si)divorced eutectic phases,and eutectic Si phase was in strip form.Compared with traditional cast aluminum alloys,its micro-hardness and compressive strength was increased by about 30% and 16%.Wear mechanisms were abrasive wear and oxidative wear.When alloy soaked in 3.5 wt.% Na Cl medium,corrosion resistance of alloy was poor,eutectic Al phase had high dissolution rate.After adding Y,phases of alloy were unchanged,but the growth morphology of eutectic Si phase changed to fibrous structure.Alloy’s density increased,while its surface roughness value decreased,surface quality was better.At the same time,micro-hardness and compressive strength were both increased by about 15%.Alloy has better abrasive wear resistance,wear volume reduced by 14% and friction coefficient was relatively stable,with 19% decrease in its value.Also corrosion pits on the surface were reduced and corrosion resistance was improved.Besides,added element Nb on the base of Al-Si-Mg-Y can reduce the size of primary α-Al dendrites and distribute them uniformly.When Nb addition exceeded 0.6 wt.%,Al3 Nb phase began to separate out from Al matrix.With the increase of Nb content,density gradually increased,surface roughness decreased,micro-hardness and compressive strength gradually increased,wear volume and friction coefficient decreased,also wear resistance and friction reduction improved.When addition of Nb was 1.0 wt.%,alloy had optimal surface quality,micro-hardness and compressive strength were increased by more than 20%,and wear volume was reduced by 78%.After addition of Nb element,alloys had distinct etching trace,corrosion resistance of alloys were greatly improved.