Abstract: In order to study the effects of different specimen shapes on the friction hydro-pillar processing (FHPP) forming of aluminum alloys， 7075 aluminum alloy was selected as the experimental object， and the ABAQUS finite element software was used. The numerical simulation of the complex thermo-mechanical coupling process of FHPP was simplified to a two-dimensional axisymmetric model and analyzed with FRIC subroutine and grid remeshing technique. By comparing the temperature cloud， deformation and stress distribution， the results showed that the shape of the specimen can affect the forming of welding defects and the defect size， the shape of the welding hole has a greater impact on the welding defect than the shape of welding rod and the fillet can be very good to prevent the forming of welding defects， the rectangular weld hole has the largest effect on hindering the fluidity for plastic metals， the chamfer weld hole has a second influence， and the fillet weld hole has the least influence which leads to better welding quality.

Key words: FHPP(friction hydro-pillar processing), specimen shape, thermo-mechanical coupling, 7075 aluminum alloy, welding defect