PURPOSE: To obtain an Al alloy for a structure with superior strength, weldability and machinability by specifying the composition of an alloy consisting of Si, Mg, Mn, Zn, Sn and Al.

CONSTITUTION: An Al alloy consisting of 2.3W6% Si, 0.4W1.0% Mg, 0.4W1.0% Mn, 0.05W0.4% Zn, 0.01W0.06% Sn and the balance Al with impurities has superior strength, corrosion resistance, weldability, machinability, etc. and can be used as a material for various structures, a material for a welded structure, a material for cutting, a material for a forged rod, etc. Si among said alloying components contributes to the increased strength and enhances the wear resistance and machinability. Mg, Zn, Mn, etc. also contribute to the increased strength. In spite of said very small amount, Sn accelerates the artificial aging and precipitates finely an intermediate pahse β', thereby increasing the strength, and it is effective in enhancing the machinability. Impurities such as Fe, Cu, Cr, Ti and B may be contained if the contents are low.