Effects of deformation on annealing and precipitation behavior of aluminum alloys.

摘要

Several commercial aluminum alloys were used to study the effects of deformation on their annealing and precipitation behavior. The alloys were solution heat treated and quenched. Deformation was made by rolling at room temperature with reductions from 0% to 90%. Annealing was subsequent to cold rolling, annealing temperatures from 100{dollar}spcirc{dollar}C to 400{dollar}spcirc{dollar}C and annealing times from 0.5 hour to 24 hours. Conductivity and microhardness were used to measure the changes of properties after cold rolling and annealing. Microstructural evolution was carried out by using optical microscopy (OM) and transmission electron microscopy (TEM).; The supersaturated heat-treatable (precipitation hardening) Al-4wt% Cu, 2024, 6061 and 7475 aluminum alloys had hardening rates higher than those of non-heat-treatable aluminum alloys. As previously reported the strain hardening of aluminum alloys was increased by high solute levels. The increased microhardness {dollar}Delta{dollar}H was found to be described by {dollar}Delta{dollar}H = K{dollar}varepsilonsp{lcub}rm n{rcub}{dollar}, and K increased as the solute increased. On low temperature annealing, there was little loss of strain hardening by recovery until the electrical conductivity rose, indicating precipitation. Measurement of decreasing electrical conductivity and rapid strain hardening, especially in 7475 aluminum alloys, appears to indicate that GP zones formed during cold rolling. The conductivity of naturally aged 7475 aluminum alloys decreased after cold rolling--indicating that the GP zones are essentially stable during deformation.; After applying high reduction ({dollar}ge{dollar}60%) of cold-rolling prior to aging, no significant precipitation hardening was found on aging the 4 heat-treatable aluminum alloys. From TEM observation, round-shaped precipitates were found in alloys with 90% reduction and rod or plate-shaped precipitates were found in undeformed alloys.; By using OM and TEM, it is confirmed that true recrystallization did not occur in heat-treatable Al-4wt% Cu, 2024, 6061 and 7475 aluminum alloys when annealing temperatures are below the solvus temperature. The subgrains appear to coarsen by extended recovery.