Abstract: 2A12 aluminium alloy was welded by the friction welding under different friction pressure. The microstructure of welding zone was analyzed by optical microscopy and electron backscattered diffraction technique. The influence of the friction pressure on the mechanical properties of the joints was discussed. The results show that the dynamic recrystallization occurred in the welding zone, grains were refined and predominantly bounded by high angle boundaries. The tensile strength of joint increased first and then decreased with the increase of friction pressure. When the friction pressure was 60 MPa, the tensile strength was maximum and the value was 412 MPa. The distribution of microhardness all showed "W" type under different friction pressure, and soften behavior appeared in heat affected zone because of the transformation and coarsening of the strengthening phase S'.