Change in electrical resistivity on ageing for Al-Cu alloys containing Cd or In

Abstract

Change of clectrical rcsistivity during ageing was measured on Al-Cu alloys containing Cd or In, and the other, further containing Mn as an additional element. Some differences were found in the effects of additional elements on change in electrical resistivity during ageing.It is well known that the addition of Cd, In, or Sn accelerates the rate of artificial ageing, but retards the rate of natural ageing. As expected from the above fact, the temperature at which abrupt decrease of resistivity took place in isochronal ageing was lower in ternary alloys than in binary. Electrical resistivity continued to fall up to about 310°C under the conditions of the present experiments and there was found no difference between the two kinds of ternary alloys (Al-Cu-In and Al-Cu-Cd alloys) in that range of temperature. Electrical resistivity change in Al-Cu-In alloys for isochronal ageing at above 310°C was similar to that in binary alloys, but was different from that in Al-Cu-Cd alloys. The increase in electrical resistivity occurred at above 310°C, but the degree of increase was larger in the latter than in the former. In the temperature range from 310 to 400 and tens of °C, electrical resistivity could be explained by the combined effect of an increase due to re-dissolution of intermediate phase and a decrease due to precipitation of equilibrium phase. Therefore, the results of the present experiments suggest that the formation of equilibrium phase would be more difficult in Al-Cu-Cd alloys than in Al-Cu-In alloys.At the early stage of isothermal ageing, an increase in electrical resistivity occurred at temperatures lower than 150°C in Al-Cu-In alloys. The above both temperature were rather lower than those claimed by Holmes et al. These temperatures can be elevated to some extent by the addition of Mn to the ternary alloys, though the rate of artificial ageing was retarded.