Research On Production Process And Properties Of Al-12.7Si-0.7Mg-xRE Welding Wires

Al-12.7Si-0.7Mg extruded section is a new type of containing magnesium and high-silicon with heat treatable and deformation aluminum alloy independently developed by Northeastern University.Aim at the welding problem of this new alloy,Northeastern University has successfully produced an Al-12.7Si-0.7Mg welding wire with the same composition as the new alloy.In this study,based on the chemical composition of the original welding wire,adding different mixed rare earth elements(Ce+La)in Al-12.7Si-0.7Mg welding wire was designed to improve the mechanical properties of aluminum-silicon alloy joints.Firstly,adding different rare earth elements content in cpl.6 mm Al-12.7Si-0.7Mg welding wire was prepared by vertical semi-continuous casting-homogenization annealing-hot extrusion-multi-pass drawing process.Study the Effect of mixed rare earth on the microstructure and mechanical properties of as-cast,extruded and welding wires in the preparation of Al-12.7Si-0.7Mg-xRE welding wires.Secondly,Al-12.7Si-0.7Mg alloy hot extruded section welded by Al-12.7Si-0.7Mg-xRE welding wires,analyze the effect of mixed rare earth on microstructure and properties of joints with before and after T6 heat treatment,provides experimental basis for the composition design of contain magnesium and highsilicon aluminum alloy with matching welding wires and aluminum-silicon welding wires for arc additive manufacturing.The preparation process of Al-12.7Si-0.7Mg-xRE aluminum alloy wires shows that vertical semi-continuous casting-homogenization annealing(520?/12 h)-hot extrusion(hot extrusion temperature 470?,extrusion the ratio of 17.36)-multi-pass drawing(11 passes of the drawing,between each pass with 400?/2 h intermediate annealing)successfully produced Al-12.7Si-0.7Mg-xRE welding wires.Adding mixed rare earth elements in Al-12.7Si-0.7Mg alloy improved the as-cast,extruded state and welding wires microstructure at some extent.The number and size of bulk primary silicon phases decreases;the eutectic silicon phase gradually changes from needle-like or long strip to short rod or granular,and the distribution is more uniform;the coarse ?-Al secondary dendrite spacing decreases.The alloy with 0.6%mixed rare earth has the best metamorphism effect,and the correspond of as-cast,extruded and welding wire have the highest tensile strength,which are 263 MPa,252 MPa and 181 MPa,respectively.The joints by Al-12.7Si-0.7Mg-xRE aluminum welding wire with different mixed rare earth elements content were formed well without macroscopic welding defects.The addition of mixed rare earth elements causes the ?-Al dendrites in the welding zone to gradually become equiaxed dendrites,and the eutectic silicon phase is refined,and the mechanical properties of joints are improved.When the mixed rare earth addition amount of the aluminum welding wire is 0.6%,the eutectic silicon phase of the welding zone is the smallest,0.88 ?m,the tissue distribution is the most uniform,and the microhardness and tensile strength of the welding zone are the highest,respectively 89 HV And 245 MPa.After the joint by T6 heat treatment,the micron-sized eutectic silicon phase in the welding zone is spheroidized and dispersed in the ?-Al matrix.When the mixed rare earth addition amount of the aluminum welding wire is 0.6%,the eutectic silicon phase of the welding zone is the smallest,1.24 ?m.The microhardness of joints welding zone by the Al-12.7Si-0.7Mg welding wire without the addition of mixed rare earth elements is lower than the microhardness of the base metal zone,and the burning of Mg element during the welding process lead to this experimental phenomenon.The main reason is that the microhardness of joint welding zone by Al-12.7Si-0.7Mg-xRE welding wires with mixed rare earth elements is higher than that of the base metal zone,and the mixed rare earth element promotes the nano-sized needle-shaped Mg2Si precipitation strengthening phase particles by desolvation and precipitation is the main reason for the improvement of microhardness in the weld zone.The mechanical strength of joint after T6 heat treatment is obviously improved compared with that without heat treatment.The joint tensile specimens welded by Al-12.7Si-0.7Mg-0.6RE welding wires with 0.6%mixed rare earth are broken in the fusion zone and heat affected zone.The tensile strength is the highest,337 MPa,and the elongation is 8.3%.