| It will be an effective method to replace a single piece of steel with steel/aluminum structural parts in order to achieve lightweight vehicle structures, which have attracted continuously interest in modern means of transport applications. With anvantages of deep welding speed, process stability, high energy density, small welding deformation, etc., laser welding has become an important method for steel/aluminum quality and efficient connections, but when the laser deep penetration welding, Fe and Al inside the pool easily generate Fe-Al intermetallic compounds, and the deterioration of steel/aluminum joint mechanical properties. This paper selects DP590duplex steel and6016aluminum alloy as the research object, the steel/aluminum are lapped, laser deep penetration test with/without the powder addition in the program, using optical microscopy (OM), SEM with EDS and EBSD probe, X-ray diffraction (XRD), computer-controlled electronic universal testing machine, the weld formability, the microstructure of each region, fracture morphology, the main phases, phase distribution, content, grain size, and mechanical properties of joints were studied to explore the mechanism of powder addition on the basis of weld formability, weld puddle metallurgical process and weld tissue change, the findings expected to provide theoretical basis for the steel/aluminum structural parts for laser welding application.Based on the characters of low melting point, high boiling point, easily melted, less volatile, Sn was added to the steel/aluminum, can change the weld puddle metallurgical process and the weld microstructure, Zr as a filler metal, can refine the grain size in weld zone, and the amount related to literature, to determine Sn-5%Zr powder as steel/aluminum layer of adding material; Based on1.4mm thick of DP590duplex steel and1.2mm thick of6016aluminum alloy plate specimen, Sn-5%Zr powder was added for lap deep penetration test, the powder was found to increase steel/aluminum interface weld width, reducing the depth of the lower melting aluminum, changing the way of the pool liquidity, weakened the stirring of the pool from laser, hinder the stirring of Fe, Al that mixed with each other, so that reduced the reaction of Fe, Al, thereby enabling the formation of a layer thickness of Fe-Al intermetallic compound is reduced; In addition, the powder together with the upper interior of the steel bath changed the molten alloying elements composition, thereby affecting the behavior of the interface and the type, morphology of phases, without powder addition, steel/aluminum interface are mainly FeAl2, Fe2Als and FeAl3, and with the powder addition, in addition to the newly-formed FeSn,Fe3Sn has good ductility, and refinement of ZrAl3, the interfacial layer of Fe-Al intermetallic compounds relative proportion of ductile brittle phase changes, which reduce the Al-rich phase, iron-rich phase increases; With no powder addition, compared with the base metal, the average grain size of ferrite,martensite are larger in weld zone, uneven distribution, the phase fraction changes a lot; when powder added, the average grain size of ferrite and martensite in weld zone are reduced, better distributed, with little change in phase fraction, there is no deterioration of phase composition in the upper duplex steel with powder addition. Because of addition of Sn-5%Zr powder increased the effective contact area, improved the bonding rate, reduced the Fe-Al intermetallic compounds layer thickness, and the newly formed FeSn, Fe3Sn has good ductility, and refinement of ZrAl3, thus the powder improved the mechanical properties of deep steel/aluminum laser welding joints. |
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