PURPOSE: To facilitate blackening treatment to an aluminum alloy for improving its heat absorbing effect and to improve its strength, machinability and formability by incorporating Mg into an Al alloy adding Cu, Mn and Fe thereto to regulate its compsn. to a specified one.
CONSTITUTION: This Al-alloy contains, by weight, 0.1 to <0.4% Fe, 0.15 to 0.6% Cu, 0.6 to 1.5% Mn, 3.0 to 5.5% Mg, <0.5% Si and the balance Al. In this alloy, Mg is heated and oxidized to form a black oxidized film essentially consisting of Mg on the surface of the alloy; in the case of less than the lower limit, the above film can not be stably formed, long time is required for blackening treatment and its strength is made insufficient; and in the case of more than the upper limit, its workability is deteriorated. As for Fe, the lower limit or above is added because it improves its drawability and improves its machinability together with Mn, but in the case of more than the upper limit, its corrosion resistance is deteriorated. As for Cu, the lower limit or above is added because it improves its strength and machinability and promotes its blackening, but in the case of more than the upper limit, its corrosion resistance is deteriorated. As for Mn, the lower limit or above is added because it improves its alkali etching properties together with Fe, but in the case of more than the upper limit, its cold formability is deteriorated.
KAITA KAZUHIRO
TAKEZOE OSAMU
