The lap welding of the 4 mm thick 7N01P-T4 Al alloy sheet and 5 mm thick Cu sheet was performed by electric beam welding.The effects of welding speeds on interfacial microstructure and performance of lap joints were investigated.The results reveal that with the welding voltage of 65 kV

the welding current of 60 mA and the focusing current of 445 mA

obvious cracks in the joints can be observed at the speeds of 600 mm/min and800 mm/min.When the welding speed is 1 000 mm/min

the sound lap joint can be obtained.A layer of Al

2

Cu intermetallic compound and a very fine（α-Al+Al

2

Cu）eutectic structure can be generated at the Al-Cu interface in the Al-Cu joint.In the Al side of the joint

the weld zone is mainly composed of the larger（α-Al andα-Al+Al

2

Cu）eutectic structure.In addition

the joints load obtained at this speed reaches 2.05 kN

and it is fractured in the weld zone of Al side.