316L stainless steel and 6061 aluminum alloy with the thickness of 0.3 mm were jointed by using YAG laser welding method.In order to improve the metallurgical bonding characteristics of aluminum and steel,stainless steel was plated with a Cu coating.Welding effects of aluminum/steel were compared before and after copper plating.Microstructure,fusion effect,element distribution and fracture morphology of welding joints were studied by optical microscope,scanning electron microscope,energy dispersive spectrometer.The results show that when the welding conditions were welding current of 130 A,laser pulse width of 4 ms,laser frequency of 13 Hz,welding speed of 150 mm/min,the gas flow rate of 25 L/min and defocusing amount of 0mm,the appearance and quality of the welding joint were good.The Cu-coating layer as transition layer of aluminum and steel welding can slow down liquid metal transfer of the interface and suppress the fusion between iron and aluminum,thus the fusion line between aluminum and steel shifts to the steel side.Microstructure analysis shows that,before copper plating,the welding joint is composed of Fe2Al5 near the aluminum side and the FeAl near steel side.However,after copper plating,the welding joint is composed of (Fe,Cu)2Al5 and (Fe,Cu)3Al due to the dissolution of Cu.Tensile fracture morphology of the welding joints are similar before and after copper plating,but the strength of the welding joint increases about 40.32%,and reaches 15.63 N/mm.