Study On Plasma-MIG Hybrid Weld Process And Properties Of 7075 Aluminum Alloy Welded Joints

The aluminum alloy materials commonly used in high-speed-vehicle car body weld structures are mainly 5××××,6×××,7××× aluminum alloys,such as 5083,6005A,and 7005.7075 aluminum alloy is an Al-Zn-Mg-Cu heat-treatable superhard aluminum alloy,which has the advantages of low density,high strength,good toughness and corrosion,etc.It is the highest strength metal in aluminum alloy materials.The application of 7075 aluminum alloy to the weld structure of aluminum alloy car body further facilitates the lightweighting of the vehicle body,reducing energy consumption,and increasing the operating speed.At present,when weld aluminum alloys in the field of vehicles,the main weld method is still the MIG weld.Compared with MIG weld,plasma-MIG hybrid weld has the advantages of high speed weld,stable weld process,no spattering,low poroosity,low heat input,narrow heat affected zone and small weld defirmation,etc.It is mainly used for the weld of aluminum and its alloys.In this paper,7075-T6 aluminum alloy as the test base material,wire ER5356,ER5183 as filler metal,the arc characteristics,droplet transfer,weld formation,weld hot cracking susceptibility and joint mechanical properties are analyzed under the plasma-MIG hybrid weld conditions.Through the high speed video and weld parameters dynamic analysis system,the arc characteristic and droplet transition behavior were studied.Under the hybrid weld,the droplet transition is mainly in the form of pulse transition and a small number of short-circuit transition,and with the increase of plasma current,it gradually turns into a pulse transition form.Through a regression orthogonal test to establish the corresponding regression equation of penetration,width and heigh of weld,and obtained the best process parameters.The brittle temperature range test was carried out according to the thermal simulation test program.The 7075-T6 brittle temperature range width is 150?.It has a high tendency to weld hot cracking susceptibility.The fish-bone test and weld plastic strain numerical calculation were tested.With the increase of heat input,the weld hot cracking susceptibility firstly decreases and then increases.The type of hot crack changes from the liquefaction crack of the partial melting zone of the base metal to the crystallization crack of the weld metal zone.When the heat input is 2.95 kJ/cm,the weld hot cracking susceptibility is minimal.Compared with ER5356 wire,ER5183 as the filler metal has the higher weld hot cracking susceptibility.Compared with conventional MIG weld,7075 aluminum alloy plasma-MIG hybrid weld has the lower weld hot cracking susceptibility.The mechanical properties of the welded joints of ER5356 and ER5183 wires were tested.The test results show that the tensile strength of the joints used in the ER5183 is higher than that of the ER5356.The tensile strength increased by 6.11%,the median fatigue strength and P=99%,y=95 fatigue strength increased by 8.3%and 10.5%.