The Microstructure And Performance Analysis Of Dissimilar Al-alloy Fillet Weld And Its Application

At present,most of the high-speed trains use lightweight aluminium alloy as the body's material in the world.In order to meet different requirements of different working conditions,and use the performance advantages of each material,a large number of interconnection components between dissimilar materials are needed in the modern engineering structures.Welding is one of the key technologies for metal connections.In this article,aiming at the fillet weld cracks between the box and the screws or fan base of the high-speed trains,we use the two different welding wires Al5356 and Al4043 to do the microstructure and performance analysis of the welded joint between the dissimilar Al-alloy 5083 and 6061.First,evaluate the weld forming,and then use metallographic method and scanning electron microscopy method to observe the organization and distribution of the scanning element of the welded joint,and test the welding heat cycle curve and microhardness and tensile property and bending property.The main results are as follows:(1)After evaluating the weld shape of using the two different welding wires and three groups of the parameters,the results are in the acceptability limits according to ISO10042-C.Analyzing from the weld penetration and throat and cross-section shape and dimensional stability,no defects were found inside the weld,and the weld shape are in the acceptability limits,and the specimen of using the 240A?12.5V?110mm/min parameters is the best in the three groups of the parameters.(2)The maximum weld penetration and peak temperature are influenced by heat input,welding torch angle or other factors,but,on the whole,the bigger heat input is,the bigger the weld penetration and peak temperature are,and the peak temperature of the base plate is a little higher than the vertical plate.In addition,the base plate and the vertical plate are different in the velocity of heating and cooling for T-joint,the base plate 6061 is higher than the vertical plate 5083 for the velocity of heating and cooling.(3)When the heat input is different,the joint microstructure is different.The nonuniform of the organization in heat affected zone increase with the distance from the weld,and the grain size is from small to big.When the heat inputs are 0.97 JmmK / ?0.98 JmmK /,the weld grain of the joint using the weld wire Al4043 are tiny isometric crystal and columnar crystal,and the second phase is separated out on grain boundary.When the heat inputs is 1.14 JmmK /,the weld joint grain is coarse,and the distribution of the second phase separated out is sparse with the increasing of the grain.the weld joint microstructure are aluminum substrate and the second phase which are skeletal and granular,and the more close to the parent material 6061 the more skeletal the second phase are,and the more close to the parent material 5083 the more the granular second phase are.The burning loss of the alloying element for the weld joint is the most when the heat inputs is 1.14 JmmK /.(4)In microhardness testing,the ruckbildung is obvious in heat affected zone of 6061 side,and the range of soften zone is 12 mm from fusion line to parent material 6061,but the ruckbildung is not obvious in heat affected zone of 5083 side.The softening degree is the highest when the heat inputs is 1.14 JmmK /.The softening degree are fairly when the heat inputs is 0.97 JmmK / or 0.98 JmmK /,and smaller than when the heat inputs is 1.14 JmmK /.In tensile shear tests,fractures locate in the weld for the joint using the weld wire Al4043,but fractures locate in the heat affected zone of 6061 side for the joint using the weld wire Al5356.On the different heat input,the weld strength is higher when the heat input is lower.With the close heat input,the weld strength is higher when the electric current is smaller.In bending tests,the weld strength is higher for the weld joint using the weld wire Al5356 than Al4043.And the bending property is best for the weld joint when the heat inputs is 1.14 JmmK /.So,the mechanical property is not bettter for the weld joint using the weld wire Al4043 than Al5356.For the microstructure,the distribution of the second phase is less for the weld joint using the weld wire Al4043 than Al5356.The welding heat cycle and welding torch angle influence the weld penetration and peak temperature and the burning loss of the alloying element for the heat affected zone,thus the heat affected zone is softened to turn into the weak zone.The ruckbildung is not obvious in heat affected zone of 5083 side,but the ruckbildung is serious in heat affected zone of 6061 side,and the hardness number is lower in heat affected zone of 6061 side than 5083 side,and fractures locate in the heat affected zone of 6061 side for the weld joint in tensile shear tests.Therefore,it should be better to use 5083 as base plate or where the force is greater in design,and it should be better to use the weld wire Al5356 which have the better performance in the process.Besides,to ensure the lower heat input is necessary.