Study On The Microstructure And Properties Of Laser High-entropy Powder-filled Welding Of Aluminum/Steel Dissimilar Metals

Aluminum/steel dissimilar metal composite components are an important lightweight structure in the automotive industry"substituting aluminum for steel".However,due to the low solubility of Fe in Al,brittle intermetallic compounds are easily generated during aluminum/steel dissimilar metal welding,reducing the mechanical properties of the joint,limiting the widespread use of aluminum/steel dissimilar metal weld joints.The high-entropy alloys formed by five or more principal elements can use the high mixing entropy effect to promote the formation of solid solutions and inhibit the formation of intermetallic compounds.Accordingly,this paper intends to introduce the high-entropy effect to the aluminum/steel dissimilar metal welding,through the high-entropy design of the weld filler material,and the use of laser high-entropy powder filler welding to increase the mixed entropy value of the weld,thereby suppressing the weld generating an intermetallic compound.Relevant research is of great significance for improving the safety and reliability of aluminum/steel welded joints and improving the lightweight manufacturing level of my country's automobile industry.Firstly,the high-entropy-designed Ni Cr Mn Si_0.5Cu Ti_0.5 filling powders were used to carry out laser powder filling lap experiments on DP780 dual-phase steel and 5083 aluminum alloy.The evolution law of powders welding butt weld microstructure.The study found that the high-entropy powders filling significantly reduce the Fe content in the weld zone,and the Fe-Al intermetallic compound in the weld is significantly reduced.The weld zone changed from the martensite structure of the non-powdered sample to the equiaxed morphology of the high-entropy powdered sample,and the grain refinement effect of the weld was obvious.However,because the high-entropy powders cannot be filled to the lap interface at the bottom of the weld during the lap joint,high entropy cannot be achieved in this area,and there are a large amount of Fe Al₂ and Al₂Cu intermetallic compounds.Then,the CoZnCuMn_0.8Si_0.2 high-entropy filling powders were used to realize the butt connection of 304 stainless steel and 6061 aluminum alloy dissimilar metals through laser high-entropy filling powders,and to explore the effect of post-weld heat treatment on the microstructure of high-entropy welds and welding interfaces The law of evolution.The study found that annealing at 280°C after welding can significantly promote the diffusion of elements at the weld interface of the high-entropy sample,and increase the Fe element content at the edge of the weld on the aluminum side.The post-weld heat treatment significantly increases the width of the transition zone on the aluminum side,from?3.4?m for the unheated sample to?16.5?m for the 6-hour sample.Post-weld heat treatment significantly increases the size of intermetallic compounds in the transition zone.It is found that post-weld heat treatment is not an effective method to control the microstructure of high-entropy welds and welding interfaces.Finally,when CoZnCuMn_0.8Si_0.2 powders welding 304 stainless steel and 6061aluminum alloy dissimilar metals,change the laser power,explore the influence of welding process parameters on the high-entropy microstructure and joint performance of aluminum/steel dissimilar metals,and reveal the realization of laser high-entropy Effective measures to control the microstructure and performance of the welded seams of aluminum/steel dissimilar metals.The study found that the laser welding power has a significant effect on the content of each element in the high-entropy weld.When the welding power is reduced from 500 W to 400 W,the Al content in the weld area decreases significantly,and the width of the transition zone decreases by 12%.And the phase structure in the transition zone evolved from Fe Al₂ and Fe Al₃ of 500 W sample to Fe Al₂ of 400W sample.The microhardness of high-entropy welds of aluminum/steel dissimilar metals is 486?500HV_0.1,which is much higher than the microhardness of 304 stainless steel base metal.The high-entropy welds have good corrosion resistance and salt resistance.The corrosion resistance to acid is similar to that of the 304 stainless steel base material.