Effect of temper, specimen orientation and test temperature on tensile and fatigue properties of wrought and PM AA6061-alloys

Abstract

The tensile and fatigue crack growth properties of 6061 Al alloy fabricated by powder metallurgy (PM) and ingot metallurgy (IM) routes have been evaluated at temperatures ranging from 25 to 300 °C. At 25 °C, the PM alloy possesses a higher strength, higher strain hardening rate and a lower elongation than the IM alloy. Raising the testing temperature from 25 to 200 °C greatly reduced the advantage in strength of the PM alloy over that of the IM alloy. At 300 °C, both alloys possess similar strength. The fatigue crack growth resistance in the TL orientation is inferior to that in the LT orientation for both alloys in T4 and T6 tempers. The difference in resistance is evident at low stress intensity in the IM alloy and is believed to be resulted from the interaction between grain size and plastic zone size, and at high stress intensity in the PM alloy which is attributable to the difference in fracture toughness. The difference in crack growth resistance between the two orientations decreases with increasing temperature and is basically non-existent at 300 °C. Furthermore, the fatigue crack growth resistance in the T6 temper is superior to that in the T4 temper. In both alloys, fatigue crack growth resistance decreases with increasing temperature. Such decrease is more prominent from 25 to 200 °C and from 250 to 300 °C. At all temperatures, the PM alloy always has an inferior crack growth resistance as compared to the IM alloy.