High Strength 2x24 Aluminum Alloy Sheet Metal Fatigue Characteristics

2024,2524,2524-Zr and 2524-Sc-Zr alloy ingots were produced by semi-continuous casting technique.It was investigated that the applied properties of 2024,2524,2524-Zr and 2524-Sc-Zr alloy sheets and their related micro-mechanism using comparative study method.Meanwhile optical microscope,transmission electron microscope and scanning electron microscopy were employed.This study included fatigue properties and macro-crack propagation,especially their related micro-mechanism.The following are important results:(1) The fatigue strength and fatigue lives of 2524 alloy sheet is higher than that of 2024 alloy sheet at the same temperature and initial stress ratio R=0.1.The fatigue strength of 2524 alloy at 10⁷ cycles was 180 MPa and 2024 was 150 MPa,respectively.(2) The addition of Zr to 2524 alloy increases the fatiugue strength and fatigue lives.The fatigue strength of 2524-Zr alloy was 185 MPa and 2524 alloy was 180 MPa,respectively.(3) The addition of Sc and Zr to 2524 alloy increases the fatiugue strength and fatigue lives.The fatigue strength of 2524-Sc-Zr alloy at 10⁷ cycles was 190MPa and 2524 alloy was 180 MPa,respectively.(4) Fe and Si exist as 2024 and 2524 alloys,one is a coarse Al₇Cu₂Fe impurity phase,and another is aluminide congtaining Fe,Mn and Si,the amount of the impurity phase in 2024 alloy is more than that in 2524 alloy,and the impurity phase of 2024 tend to accumulate.(5) The space between fatigue striations on the hing frequency axial fatigue fracture of 2024 alloy is wider than 2524 alloy.Impurity phases was easily found near the fatigue crack source around which crack easy occur because the impurity phases is very brittle and decrease the fatigue strength and fatigue lives.(6) In 2524-Sc-Zr alloy,the nucleation and growth of micro-crack are impeded effectively by the fine grain structure,dispersion Al₃(Sc,Zr) particles,high-density dislocation and grain boundary,high resistance force of dislocation motion,these are the main causes that lead to higher fatigue lives and fatigue strength for the 2524-Sc-Zr alloy.