Improvement of 319 aluminum alloy casting durability by high temperature solution treatment

The purpose of this paper was to investigate the effect of one and two stag e solution treatment on the mechanical properties of the 319 aluminum alloy , and to determine the effect of strontium addition on the characteristic t emperatures of copper-rich eutectic phases. For an alloy containing 18 ppm strontium, it was found that traditional single-step solution treatment (49 5 degreesC/8 h) did not produce optimum mechanical properties because it di d not maximize the dissolution of copper rich phases, nor was it able to su fficiently modify the silicon particle morphology. A two-step solution trea tment process, however, was capable of accomplishing these goals and is the refore recommended. The optimal two-step solution treatment, for the alloy investigated, involved a first step at 495 degreesC for 2 h followed by a s econd step at 515 degreesC for 4 h. This solution treatment was followed by water quenching to 74 degreesC and artificial aging at a temperature of 25 0 degreesC (for 3 h). Strontium addition appears to raise the characteristi c temperatures of copper-rich eutectic reactions. Therefore, it is likely t hat in higher strontium content aluminum alloys, a higher temperature two-s tep solution treatment would be required to optimize casting mechanical pro perties. This hypothesis will be investigated in a forthcoming paper. (C) 2 001 Elsevier Science B.V. All rights reserved.