Research On The Effect Of Modified Alloy Al-Ti-Sr-La On Processing Performance And Weld Mechanical Properties Of SAl4043 Welding Wire

With the expansion of application fields of aluminum alloy materials and the improvement in performance indexes,the demand for aluminum alloy welding materials is further increased.Among them,the main alloy elements of the 4-series alloy welding material are Al and Si.Al-Si alloy has a low melting point and wide crystallization temperature range,which makes the welding material have good fluidity after melting,small shrinkage rate during solidification,less possibility of crystal cracks,and excellent crack resistance and welding performance.Therefore,the market has a strong demand for this kind of Al-Si welding material with wide applicability and excellent weldability,especially the SAl4043 welding wire with a Si content of 5-6%.wt,but the coarse eutectic in the Al-Si alloy The characteristics of silicon structure and aluminum-silicon alloy's easy hydrogen absorption have always restricted the application of Al-Si welding materials to high standards and high reliability.At the same time,higher requirements have been placed on the production and processing technology of welding materials.Starting from the smelting process of welding wire preparation,the traditional Al-Si welding wire alloy is refined and modified by the prepared new composite modified alloy.The influence rule of Al-x Ti-y Sr-z La new intermediate alloy on optimizing the microstructure of welding wire alloy and improving the machinability and welding performance of SAl4043 aluminum alloy welding wire is systematically studied,which effectively improves the purity and uniformity of welding wire alloy structure,greatly improves the machinability of SAl4043welding wire,and lays a solid foundation for obtaining high strength,high plasticity and low hydrogen welding seam.The orthogonal test method was used to design 9 groups of Al-x Ti-y Sr-z La intermediate alloys with different distribution ratios.The mechanical properties,hydrogen content,and microhardness of the aluminum alloy wires treated with the nine intermediate alloys were investigated.Ti,Sr,and La have different degrees of influence on different performance indicators of the welding wire.According to the analysis of variance,the optimal composition ratio of the intermediate alloy was:Al-5Ti-0.5Sr-5La and Al-5Ti-0.5Sr-7.5La.Further observation of the scanning microstructures of Al-5Ti-0.5Sr-5La and Al-5Ti-0.5Sr-7.5La reveals that Ti Al3 particles,which play a key role in refining,are significantly reduced in size due to the addition of rare earth La.The size is about 30-50?m,which is 73%smaller than Ti Al3 in Al-5Ti.The main deterioration elements Sr exist as a fibrous Alx Sry Laz mixed phase,and the modification efficiency is more than the flake Al4Sr compound in Al-10Sr.Efficient.However,with the increase of the rare earth La content,the segregation effect of Ti₂Al₂₀La phase appears,which has a certain of delayed effect on the refinement of the master alloy.The?-Al phase of the aluminum alloy welding wire,which has undergone Al-5Ti-0.5Sr-5La and Al-5Ti-0.5Sr-7.5La modification and refinement treatment,is composed of many fine grains and some dendrites and equiaxed crystals.The grain sizes are 32.2?m and 41.5?m,respectively.Under the dual metamorphism of Sr and rare earth La,eutectic silicon transforms from undeformed needle-like morphology to fine-grained morphology and is uniformly distributed in the?-Al phase In the world,the average size of eutectic silicon is 83.8%and 87.6%smaller than that of unmodified eutectic silicon,respectively.Through spectroscopy analysis,it was found that acicular La-rich phases with Alx Siy Fe2La as the main component appeared in Al-Si alloys modified with Al-5Ti-0.5Sr-5La intermediate alloy.When Al-5Ti-0.5Sr-7.5La master alloy is used,another massive La-rich phase is formed.The coarse needle-like?-Fe phase of rare earth La is the fishbone?-Fe phase,which obviously improves the microstructure and morphology of the alloy.However,when the rare earth La exceeds 0.1wt.%,the phenomenon of"autophagy"occurs,that is,the needle-like?-Fe phase appears again,resulting in a decrease of the microstructure and properties of the alloy.The solid hydrogen content test,weld porosity calculation and mechanical property test were carried out on the modified welding wire alloy of Al-5Ti-0.5Sr-5La and Al-5Ti-0.5Sr-7.5La and the weld seam welded by the welding wire,respectively.The results show that the hydrogen content of the welding wire and the weld seam porosity have obvious genetic effects.The hydrogen content of the modified alloy wire is 0.22 m L/100 g Al and 0.14 m L/100 g Al,respectively,which are 47.6%and 66.7%lower than the undegraded wire,and the WPP of the undegraded wire is 0.58%,which exceeds the allowable,the maximum WPP value was 0.5%,while the WPP value of the deteriorated wire decreased by 20.7%and 36.2%.The bending test results of the weld obtained from untreated welding wire are unqualified in 180 positive and reverse bending tests,and the weld center is high in hardness and poor in plasticity.It is easy to become a weak point and lead to a fracture in the stretching process.The bending test of the modified welding wire is qualified.The lowest point of the microhardness of the weld is located in the HAZ region,which is consistent with the tensile fracture position.This shows that the tensile strength and elongation of the modified welding wire are obviously better than those of the unmodified weld.Therefore,the addition of a new intermediate alloy can effectively improve the mechanical properties of the weld joint.