In this paper, AA5083-H112 aluminium alloy and T2 pure copper were LFW welded with no obvious defect under different forging pressures. The microstructure and mechanical properties were investigated by SEM, hardness and tensile tests. The results showed that “friction effect” would increase with the decrease of the forging pressure so that more Cu particles infiltrated into the Al base metal, while with the increase of the forging pressure, the tensile property dropped significantly because rising of the forging pressure could supply more heat input so that layered Al₂CuMg phase came out which was harmful to the tensile strength of the welds.