Development of Aluminum Recycling Technology

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This study was conducted for the purposes of searching a useful element for the removal of impurities such as Bi, Si, Fe ets. expected to be mixed when recycling aluminum alloys and for determining the tolerance limits of impurities satisfying various properties of the wrought Al-Mn and Al-Mg-Si alloys specified by JIS.Solidification behavior, and effects of impurities on mechanical properties, formability and corrosion resistance of the recycled commercial aluminum alloys were investigated from the view point of metallography. (1) Giant intermetallic compounds with sizes of over 10 mu m crystallize when 3d transition elements such as V and Mn are added to 6061 and 6063 aluminum alloy melts. The compounds are Al_6Mn or alpha -Al (Mn, Fe) Si phases replaced by other elements on occupying sites of Mn and Fe in their crystal structures and they settle at the bottom of the crucible during a short time due to their larger specific gravity than that of aluminum melt. (2) In Al-Mn (3003) allo … More y, increases in contents of Bi and Ca cause no changes of tensile strength and 0.2% proof stress, but decreases in elongation, Charpy impact value, formability and corrosion resistance. Particularly, a coarse CaAl_2Si_2 compound increases with increasing Ca content, resulting in the drastic degradation of elongation and impact value. Therefore, amount of Ca remained in the 3003 alloy should be less than 0.1%. (3) In Al-Mg-Si (6061) alloy, tensile strength and 0.2% proof stress are markedly lowered because crystallized compounds increases with increases in V,Mn and Ca contents. The compounds largely contain silicon which contributes to age hardening in 6061 aluminum alloy. Elongation and impact value are degraded due to the existence of the coarse compound in the V-containing alloy ; unchanged in the Mn-containing alloy ; and upgraded due to softening of matrix phase and the fine-distributed compounds in the Ca-containing alloy. There is no effect of Zr content up to 0.3% on the various properties of 6061 aluminum alloy. It's required that V,Mn and Ca contents in 6061 aluminum alloy are less than 0.2%, 0.4% and 0.1% respectively to guarantee tensile properties satisfying JIS values. Less