TIG surface remelting was performed to strengthen the surface of ZL109G alloy piston. The macrostructure indicates that surface remelting leads to the production of a remelted zone (RZ). The diameter of the primary Si decreases from 65.8 μm in the base metal (BM) to 7.1 μm in RZ. The grain size of the RZ is refined to be approximately one-seventh that of the BM. The cellular microstructure in the RZ is characterised by the α(Al) in the centre and intermetallics preferentially located at the cellular boundaries. The results of the mechanical properties demonstrate that the average hardness value of RZ increases by 39% compared to that of BM. For the transverse samples, the ultimate tensile strength increases by ~24.5%, which can be attributed to the solution strengthening of Si in α(Al). The average fracture toughness values are 15.0 and 12.7 MPa·m^1/2 for α(Al) in BM and RZ, respectively.