Hard coated copper alloys

A coated copper alloy which comprises a copper alloy having a surface coating containing Sn, said Sn coating being formed by surface treating said copper alloy with Sn, followed by heat treating the resultant Sn coated copper alloy to cause heat diffusion so as to form a surface coating consisting essentially of Cu and Sn, said surface coating extending to a depth which includes at least the resultant interface between the Sn-containing layer and said copper alloy, said surface coating having a thickness of 1 to 5 .mu.m, wherein the copper alloy has a composition selected from the group consisting of

• (a) 4.2 wt % Zn, 0.14 wt % Fe, 1.03 wt % Sn, 0.05 wt % P, with the remainder being Cu,
• (b) 4.1 wt % Zn, 0.18 wt % Fe, 1.94 wt % Sn, 0.04 wt % P, with the remainder being Cu,
• (c) 4.2 wt % Zn, 7.9 wt % Sn, 0.186 wt % P, with the remainder being Cu,
• (d) 4.3 wt % Zn, 0.2 wt % Mg, 0.09 wt % P, with the remainder being Cu, and
• (e) 1.9 wt % Zn, 0.15 wt % Al, 0.18 wt % Cr, with the remainder being Cu.