Influence Of Probe Shape On Material Flow Behavior And Mechanical Properties Of Al/Fe Friction Stir Welding

Nowadays,in order to save energy and reduce harmful gas emissions,the application of light metals like Al alloy is effective for achieving lightweight vehicles.However,large amount of lightweight alloys will increase the cost and reduce strength.Main structural parts have to be still steel to maintain the mechanical strength.The joining of them,however,remains a challenge due to the different physical and chemical properties.Traditional welding methods cannot meet the need for dissimilar material welding.As a new solid-state joining process,friction stir welding can be a hopeful candidate for dissimilar material joining.Generally,welding tool is composed of a probe and shoulder.The successful design of welding tool is the key to FSW,which will directly affect the material flow behavior during FSW and the quality of the welded joint.Therefore,it is of great significance to study the influence of welding tool shape on material flow behavior and mechanical properties of dissimilar material FSW.In this study,the usage of PVC material to simulate A1 alloys and quartz glass to simulate steel can effectively realize the material flow visualization in Al/Fe dissimilar FSW.By comparing the result of PVC simulation experiment and the result of A6063/S45C FSW experiment,the influence of three probes with different surface structure,coarse screw probe,flute probe and fine screw and flute probe,on the material flow behavior and mechanical properties of Al/Fe dissimilar metal FSW.The research indicates that fine screw and flute probe is better than coarse screw probe and flute probe in the case of Al/Fe dissimilar material FSW.Comparing to screw probe and flute probe can promote material flow in horizontal direction and depth direction separately,fine screw and flute probe can promote material flow both in depth direction and horizontal direction,expanding stir zone effectively.During FSW,the scroll shoulder can apply a downward forging force.It governs to constrain and fill material in welding line.At the beginning of FSW,scroll shoulder gathers the material to the center of welding tool.Then the materials flow along the probe surface structure and extrude from the edge of probe,flowing from advancing side(AS)to retreating side(RS).Therefore,the closer the material flows to the surface of the welding material,the lower the speed.When using fine screw and flute probe,the material flow velocity on AS is about 20 mm/s and the velocity on RS is about 30 mm/s.Comparing to other two probes,it can increase the material flow velocity moderately and it is better for the scroll probe to maintain the stability of welding progress,forming a flat and smooth welding line.In the case of fine screw and flute probe,the fine screw structure governs to create a new interface on the steel side,expand the contact area of plasticized Al alloys on the new interface.Based on the sufficient material flow,it effectively promotes mechanical combinations of plasticized Al alloys and steel.Therefore,the welding strength by using fine screw and flute probe is higher than other two probes.