| The process of Nd: YAG laser welding for 316 L stainless steel and 6061 aluminum alloy that those thickness is 0.3 mm was investigated, the experimental use sealing side of lap and joint form structure, by using the method of orthogonal experiment to optimize welding process parameters(welding current, laser pulse width, frequency, laser welding speed) of the two kinds of joint, and by using optical microscope, scanning electron microscopy(SEM) and energy spectrum analysis method to study on the joint interface, the fusion of microstructure characteristics,element distribution and fracture morphology, micro hardness tester study on the changes of hardness on interface;In order to improve the joint performance, the stainless steel processing copper plating, and study the copper element on the influence of the joint interface elements, organization distribution.Aluminum steel form of lap joint laser welding result shows that the optimized welding current was 100 A, laser pulse width was 4.5 ms, laser frequency was 12 Hz,the welding speed was 0.17 m/min.The optimized joint tensile shear strength was22.23 N/mm; in the region of the interface product Al3(Fe, Cr, Ni),(Fe, Cr, Ni)Al2,(Fe, Cr, Ni)Al intermetallic compound because of diffusion of Fe and Al;The molten iron substrate crack due to the existence of C element;Near the fusion line crack mainly due to the production of intermetallic compound and C element combination,because of rapid cooling fusion area of stainless steel and the hardness is greater than the parent metal; Near the fusion line due to the existence of the brittle intermetallic compounds, the hardness of the fusion line area is far greater than the parent metal hardness; Crack near the carbon content is higher, hardness near the crack is far greater than the parent metal. Joint form of fracture was brittle fracture along the grain boundary.Study on laser welding side joint form of Aluminum Steel shows: The biggest of unit length tensile shear load was f, was 19.79 N/mm; Optimal levels of Aluminum/steel dissimilar metal welding laser was A2B3C3D2, welding current was110 a, laser pulse width was 4 ms, laser frequency was 16 hz, the welding speed was200 mm/min., the distribution of Aluminum Steel joint interface intermetallic compound was uneven, A small amount of iron inset the aluminum substrate, IMC mainly composed by(Fe, Cr, Ni) Al that was close to the aluminum and(Fe, Cr,Ni)2Al5 that was close to steel, ?- Al and Al(Fe, Cr, Ni)3 Embedded on one side of the aluminum mainly. Due to difference of the absorptance of aluminum and steel,the fusion line and the gaps between the parent metal show "Y", Part of the joint area of stainless steel and near the fusion line have different cracks. Microhardness Near fusion line increased sharply, far greater than the hardness of weld pool;Aluminum steel dissimilar metal sealing side fracture form is mainly brittle fracture, and with a certain plastic fracture.The research of stainless steel after copper plating results show that the copper plating layer formed aluminum steel welding transition layer, reduced the liquid metal transfer, restrain the fusion between iron and aluminum, Aluminum steel fusion line offset to the steel side. Microstructure analysis shows that, before copper plating,there was Fe2Al5 near the aluminum side, and the Fe Al near steel side, respectively.However, after copper plating, there were(Fe, Cu)2Al5 and(Fe, Cu)3Al on the steel side due to the dissolution of Cu. After copper plating in the main solution to the Fe Cu, organization is mainly composed of joint interface(Fe, Cu)2Al5,(Fe, Cu)3Al composition.After copper plating the joint unit length tensile shear strength increases,the growth rate is about 20%- 40%, Growth rate of I joint was biggest,before copper plating joint tensile resistance of unit length was 11.14 N/mm, stainless steel plating copper joint after the tension resistance of unit length was 15.63 N/mm, tensile resistance increased by 40.32%.However Tensile fracture morphology of the welding joints were similar before and after copper plating. |
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