This study investigates the microhardness and corrosion properties of friction stir welded (FSW) joints in phosphor bronze (CuSn4), a vital non-ferrous alloy in engineering applications. The research delves into the FSW process, employing varying welding parameters to create joints that exhibit distinct microstructural characteristics. Microhardness distribution across the FSW joints is assessed and correlated with the base material’s properties. Corrosion behaviour is rigorously examined through weight loss tests, revealing insights into the susceptibility of FSW joints to various corrosive environments. The study identifies the influence of FSW parameters on microhardness and corrosion performance, thus contributing to understanding the alloy’s behaviour under this welding technique. This research shows that the welding speed of 0.25 mm/s, tool rotational speed of 1100 rpm, plunger depth of 0.2 mm, and a hexagonal tool profile produce the better joint with the highest microhardness of 139 HV and rate of corrosion of 0.420831 %.