The microstructure and properties of the butt joint of repair welding of 6 mm 6005 A-T6 aluminum alloy plate for railway vehicle are studied by using the rapid thermal start-up technology（RTS）. The results show that the microstructure of the original welds are dendritic crystal and equiaxial dendritic crystal

the grains are fine

and the microstructure of the weld is composed of α-Al matrix and Mg2 Si

Al0.7 Fe3 Si0.3 second phase;the original weld is affected by the weld thermal cycle of repair welding

the α-Al matrix grains begin to coarsening

and the microstructure deterioration and grain coarsening of the original weld are more serious after three times of repair welding

and more equilibrium phase precipitates out. At the common boundary of the repair welding weld and original weld

as the times of repair welding increases

the grain coarsening is more obvious and the microstructure of interface tends to deteriorate;Using once RTS（80 ℃） repair welding technology before welding

it can be more obvious to reduce the pores caused by the normal repair welding

and at the common boundary of repair welding weld and original weld

the grain coarsening is not obvious

its microstructure is superior to that of once normal repair welding. There are obvious softening zones in as-welded joint and repair welded joint

the minimum HV0.1 hardness value appears in the heat-affected zone of the original welded joint. The tensile specimens of repair welding joints break at 45°

and the fracture has obvious dimple

which is a typical ductile fracture. The strength coefficient of the original joint and the once repair welding joint by RTS is 0.6

and except the welded joint after three times repair welding

when the bending angle of welded joint is 180°

bending specimens have no cracks

and the plasticity of welded joint is good.