Effect Of Si And Zr On The Properties Of ER5356 Aluminum Alloy Wire As Well As Its Welded Joint

Aluminum and its alloys are becoming more and more important in modern industry especially in the high-speed rail, automobile and vessel industry. Because of their characteristics of lightweight, high strength, good formability, excellent weldability and outstanding corrosion resistance, aluminum alloys were praised as the preferred materials for lightweight vehicle. 5083 aluminum alloywas widely used in the manufacture ofcar body panels and reinforcement plate, and ER5356 aluminum alloy wire has been widely used in the welding of 5083 aluminum alloy. However, available domestic ER5356 wire wasunable to meet the welding requirements, due to its lower strength of the welded joint. In order to improve the weldability of ER5356 wire and the properties of 5083 welded joint, the effect of Si and Zr on the properties and microstructures of ER5356 wires and the 5083 welded joints were studied in this dissertation.The effect of Si content on the microstructures and properties of ER5356 wires and its welded joint were investigated. Results showed that Si content should not be more than 0.2wt.%, and the optimum content of Si was less than 0.12 wt.%. When the content of Si was higher than 0.12 wt.%, some coarse silicon rich phases were found in the microstructures of ER5356 wire and its weld, and all properties, especially plasticity, dropped with the increase of Si content. In particular, when the Si content was above 0.2wt.%, the coarse silicon rich phases were enriched at the grain boundaries, and forming fish-bone-shaped eutectic structure with ?-Al matrix, and their tensile properties dropped more obviously.Tests also revealed that ER5356 wire with the Si content belowing 0.12 wt.% had better surface quality after mechanical scraping, which made wire feeding more choicenesss and brought little fluctuation of the welding current and voltage.The microstructures of ER5356 wires and the 5083 welded joints were improved by Zr addition. Analysis revealed that Zr atoms preferentially reacted with Al atoms to form Al3 Zr compound during the solidification, which played a role as the heterogeneous nucleation sites of ?-Al solid solution. Whenthe content of Zr ranged from 0.05 wt.% to 0.15 wt.%, the refining effect on the grain was obvious, especially when the Zr content was around 0.1wt.%, the alloy had the best refinement effect.While the excessive content of Zr would lead to forming coarse Al3 Zr compound and Ti poisoning phenomenon, which might weaken the modification effect on the ER5356 wire and the 5083 weld.The properties of ER5356 wires and the 5083 welded joints were also improved by Zr addition. The tensile properties of ER5356 wires and the welded joints increased firstly and then decreased with increasing of Zr content. It was found that 0.1wt.% Zr addition could improve the tensile properties significantly. The tensile strength and elongation were 6.3% and 19.7% higher respectively than the welded joint without Zr addition, and the fracture type of the 5083 welded joint was ductile fracture with the best uniformity of dimples.When the Zr content was above 0.2wt.%, the mechanicalpropertiesof ER5356 wires and the 5083 welded joints dropped obviously, the surface hardness of ER5356 wires using mechanical scraping was uneven, which brought large fluctuation of the welding current and voltage, and the corrosion resistance of the welded jointsalso declined.