Effect of heat treatment (T5, T6) on the tensile and fatigue properties of Al 7003 alloy

A7003 alloy underwent T5 and T6 heat treatments (T5: 90°C for 5 hrs and 150°C for 16 hrs; T6: 470°C for 3 hrs followed by artificial aging at 80°C for 14 hrs, and 120°C for 42 hrs); the tensile and fatigue properties of the treated materials were then examined. High-cycle fatigue tests were conducted at R (stress ratio)=0.1, and f (frequency)=20 Hz. The average grain size of A7003-T5 alloy was 3.8 μm, and that of A7003-T6 alloy was 4.1 μm. Both of the alloys were found to have MgZn2 (η), Fe-based intermetallic phases in their aluminum matrix. A7003-T6 alloy had finer MgZn₂ (η) phases distributed more evenly than A7003-T5 alloy. Tensile test results showed that A7003-T6 alloy had higher strength (Y.S. & T.S.) and lower elongation compared to those of A7003-T5 alloy. High cycle fatigue results showed that A7003-T6 alloy had longer fatigue limit (320 MPa) than that (290 MPa) of T5 alloy. A7003-T6 alloy was found to perform better in all other fatigue stress conditions, too. Based on the observation of tensile and fatigue fracture surfaces, the correlations between microstructures made by heat treatments and mechanical/fatigue properties were also investigated along with the fatigue deformation mechanism of A7003 alloy.