Effect of T6-treatments on microstructure and mechanical properties of forged Al-4.4Cu-0.7Mg-0.6Si alloy
(1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education,
Central South University, Changsha 410083, China;
3. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
Abstract: Transmission electron microscopy (TEM), scanning electron microscopy (SEM), hardness tests and tensile tests were performed to investigate the effect of aging on microstructure and mechanical properties of forged Al-4.4Cu-0.7Mg-0.6Si alloy. The results show that the alloy exhibits splendid mechanical properties with an ultimate tensile strength of 504 MPa and an elongation of 10.1% after aging at 170 °C for 16 h. With tensile testing temperature increasing to 150 °C, the strength of the alloy declines slightly to 483 MPa. Then, the strength drops quickly when temperature reaches over 200 °C. The high strength of the alloy in peak-aged condition is caused by a considerable amount of θ'''' and AlMgSiCu (Q) precipitates. The relatively stable mechanical properties tested below 150 °C are mainly ascribed to the stability of θ'''' precipitates. The growth of θ'''' and Q precipitates and the generation of θ phase lead to a rapid drop of the strength when temperature is over 150 °C.
Key words: forged Al-4.4Cu-0.7Mg-0.6Si alloy; aging treatment; mechanical properties; θ precipitates