Study On Process Of Laser-heated Friction Stir Welding Of Dissimilar Metals-steel And Aluminum Alloys

A method that laser-heated friction stir welding(LHFSW) was proposed in thisthesis regard of the difficulties of welding dissimilar metals such as steel andaluminum. Laser was used to heat the steel and the friction stir tools that made ofW-Mo alloys were used in the friction stir welding machinewhich was changed bymilling machine. Then the welding joint of steel and aluminum alloys was obtainedsuccessfully.Firstly, the model of laser-heated steel was established by simulation softwareCOMSOL, and such parameters as suitable spot radius,laser power were determinedthrough simulation analysis.The model of LHFSW steel and aluminum was built tostudy the influence rule of technological parameters on the temperature field. Andthe parameters included down force, feed speed and rotate speed of friction stir tool.Then the parameters scope of down force, feed speed and rotate speed were deducedin consideration of the steel yield strength changed along with temperature andmelting point of aluminum alloys.Secondly, FSW experiaments of steel and aluminum were carried out to studythe influence of welding technology on the welding joint quality. And the weldingtechnology included the relative position of steel and aluminum, tool pin offset,dimension of friction stir tool. It was easy to obtain the welding joint ofsteel-aluminum when steel was placed in the advancing side. There was no holedefect when tool pin covered the aluminum part more than the steel part, conversely,hole defect appeared on the weld surface. The steel and aluminum material wrapedwell and the weld surface was smooth when the big tool shoulder was used. Theprebored hole could be filled well when the diameter of prebored hole was smallerthan tool pin diameter.Thirdly, LHFSW experiaments of steel and aluminum were done to study theinfluence of laser power, plunge depth of shoulder and rotate speed on the weld jointquality. Partial steel material was vaporized, so the welding quality was affectedwhen the laser power was400W to700W by manual operating. The steel wassoftened and the wear of friction stir tool was reduced when laser power wasbetween200W and300W, which indicated that the effect of preheating was better.There was groove defect on the steel surface and tool pin was worn heavily because that the plunge depth of shoulder was extremely small. It was easy to appear flawdeffect on the weld surface when the rotate speed was too high, because aluminumexceeded its melting point. However, the weld surface quality was smooth by usinglower rotate speed, because the aluminum was semisolid state.Finally, the microstructure of steel and aluminum welding joint was investigatedthrough metallographical experiaments and the mechanical property of welding jointwas studied by testing the microhardness and tensile strength.