STUDY ON THE AGE-HARDENABLE ALUMINUM ALLOYS CONTAINING BERYLLIUM

Abstract

As an attempt to enhance the strength of age-hardenable Aluminum alloys, the effect of the addition of small amount of Beryllium was investigated whether Be can increase the age-harden- ability of any Al alloy to a considerable extent or can prevent stress-corrosion to make Al-Zn- Mg alloy of more Zn content become practically useful.Firstly, small amount of Be was added to each one of the commercial Al alloys. The effect of the addition of Be was proved to be remarkable in Al-Cu system; where 0.3%Be could increase the strength of 4%Cu alloy up to the level of super Duralmin. However, the effect was found to be less in Al-Cu-Mg system. These results were discussed in relation to the changes occurred in Al-Cu or Al-S (Al5 Cu2 Mg2) diagram when be was added respectively. The corrosion resistance of Al-Cu, Al-Cu-Mg and Al-Zn-Mg alloys could be improved only slightly by the addition of Be and the stress-corrosion characteristic of Al-Zn-Mg alloy was not so much improved as well as its strength when Be was added. The Vickers hardness of Al-Zn-Cu-Mg-Be alloy, containing 8%Zn, 2%Cu, 2%Mg, and 0.2%Be will exceed 150 when aged at room temperature. But more study seems to be necessary to find suitable composition range for industrial use as the workability and stress-corrosion resistance of this system are not yet satisfiable.Secondly, nine binary Al alloys were studied, choosing Zn, Ag, Mg, Sn, Si, Mn, Ni, Sb and Cd as the second element, when 0.5%Be and 0.5%Mg were added respectively. No alloy system. however, was found to have more hardness than 100 in Vickers when fully aged, except Al-Zn-Mg-Be system already considered above. Al-Ag-Mg-Be and Al-Mg-Be system followed, but they are not satisfiable as high-strength Al alloys from the economic point of view.Other Al alloys; Al-Mg-Si, Al-Zn-Cu, Al-Cu-Mn and Al-Mg-Fe, containing 0.2%Be respectively were considered. The second and third system were found to reach the strength of super Duralmin by room-temperature ageing. Therefore, these two systems may be used commercially, if Be will become much less expensive to be got in Japan.In conclusion, several aluminum alloy sy stsms, such as Al-Cu-Be, Al-Cu-Mg-Be, Al-Zn-Cu-Be, Al-Cu-Mn-Be and Al-Zn-Cu-Mg-Be, the last one being the strongest, were found to have enough strength as super Duralumin. It will be an economic problem whether any of these systems can be used in industry. However, it seems to he extremely difficult to enhance the strength of Al alloy by the addition of Beryllium in such an epoch-making wise as in Cu-Be alloy.