The Study On Aluminum/steel Interface Layer Based On Synchrotron Radiation

In society where new energy vehicles are vigorously promoted and developed,the driving distance and power of vehicles have a demand for the weight of the vehicles weight.Because of the high specific strength,excellent electrical conductivity and good corrosion resistance of aluminum alloy,it can be used as a substitute for some traditional steel components to reduce the weight of the overall structure effectively.However,there is difficulty for the welding between aluminum alloy and steel.That is the generation of intermetallic compounds(IMCs)which are hard and brittle.Therefore,the tensile strength would be reduced seriously.Based on Shanghai Synchrotron Radiation Facility(SSRF),the paper conducted the experiments on the in situ observation of the generation and growth of IMCs to study the growth regularity of IMCs.Besides,the hot-dipping experiments of galvanized steel conducted for the comparison between the sample observed by synchrotron radiation.What's more,aluminum alloy/galvanized steel and aluminum alloy/stainless steel were welded by tungsten inert gas(TIG)welding with a flux-cored filler metal of Al-12wt.%Si to compare the difference of microstructure,tensile strength and the influence of weld reinforcement.The growth process of Fe2Al5 distributed along the interface between aluminum alloy and steel was observed based the synchrotron radiation facility and the growth orientation was towards steel and participated to the interface.However,due to the limitation of resolution and contrast,Fe4Al13 was not found.After in-situ observation,EPMA was used for the sample,and Fe4A113 was found between Fe2Al5 and aluminum alloy and that is the same as the sample used for hot-dipping.At the same time,needle-like Fe4A113 can also be found distributed in aluminum alloy.Simultaneously,FeAl was distributed along the interface of Fe2Al5 and steel with a thickness of 1 ?m for two kind of samples.Zn diffused towards steel.The thickness of IMCs is proportional to the square root of time,and the proportionality coefficient is 1.45 and 3.06 for the in-suit observation sample and hot-dipping sample,respectively.The maximum tensile strength of aluminum alloy/galvanized steel welding joints and aluminum alloy/stainless steel is 169MPa and 142MPa,respectively,which reached 81%and 68%of the tensile strength of aluminum alloy.The former joints fractured along the heat affected zone(HAZ)but the latter joints along the IMCs.When the weld reinforcement was removed,the tensile strength reduced to 34MPa and 66MPa,respectively.And two kinds of joints fractured along the IMCs.For the hardness distribution,there was not variation along the HAZ of steel for aluminum alloy/galvanized steel but increasing shapely for aluminum alloy/stainless steel which is up to 273HV.From the hardness distribution nephogram,the width of HAZ of aluminum alloy can be found clearly and the value of width was about 7mm which was much higher than the steel side.For the microstructure of aluminum alloy/galvanized steel and aluminum alloy/stainless steel,there were differences between two kind of joints.The aluminum alloy/galvanized steel weld consisted of needle-like Al-Fe-Si ternary phase and net-like Al-Si eutecticum.The aluminum alloy/stainless steel weld was made up of block Al-Fe-Si-Cr phase and net-like Al-Si eutecticum.Meanwhile,due to the wetting action of zinc coating,the IMCs of aluminum alloy/galvanized steel joints was much uniform than aluminum alloy/stainless steel joints.