Temperature effects on the tensile properties of cast and heat treated aluminum alloy A319

In this work, the tensile properties and ductility of an Al-A319 alloy were investigated as a function of temperature and heat treatment. Tensile testing was carried out at temperatures ranging from −90 to 400 °C for the alloy in (a) the as-cast condition, (b) after solid solution at 485 °C (T4) and (c) after solid solution followed by ageing at 230 °C (T7). It was found that the alloy tensile strength was improved by heat treating from 195 MPa in the as-cast condition to 305 MPa in the T7 condition. Nevertheless, the alloy elongation was relatively poor, in the 2-3% all the way to temperatures in the neighborhood of 300 °C. The low alloy ductility was found to be related to internal damage dominated by cracking of intermetallic α-Al15(Mn,Fe)3Si2 and θ-Al2Cu particles including silicon. Heat treating was found to increase the work hardening exponent, n in the σ = Kɛn expression from 0.23 to almost 0.29. Moreover, it was found that n was not severely affected by temperature for temperatures below 200 °C. However, temperatures beyond 200 °C lead to appreciable reductions and overlapping in the magnitudes of n when compared with the as-cast condition. In turn, this indicated that above 200 °C, the work hardening properties of alloy A319 imparted by heat treating tend to dissipate. Apparently, bulk precipitate coarsening coupled with alloy softening mechanisms become active and they are dominant at temperatures above 300 °C. Moreover, the fraction of cracked particles was found to increase with temperature in this temperature regime. Weibull statistics and the probability of particle cracking indicated that at temperatures below 300 °C, damage accumulation by particle cracking is the dominant mode of fracture as indicated by the slope, m = 3 of the linear Weibull plot. Depending on the alloy condition, critical particle stresses for cracking of 0.5-3 GPa were predicted using Weibull statistics.