Fatigue crack propagation behaviour of Al-Zn-Ce alloys

Abstract

A B S T R A C T This paper presents the investigation on fatigue crack growth behaviour of Al-Zn andAl-Zn-Ce alloys. Fatigue tests were carried out on as-cast and heat-treated CT specimens according to ASTM E647 testing standard. The test results showed that the addition of rare earth element (cerium) and heat treatments (T6 and T5) had very strong influence on fatigue strength. This enhancement was due to metallurgical changes in the alloy system. Cerium eliminates the porosities and refines microstructures of the alloy, showing the improved fatigue crack growth behaviour. In addition, the fatigue fractured specimens were examined using a scanning electron microscope to clarify the fracture initiation points.cycles for crack initiation N f = number of cycles at specimen failure R = load ratio (P min /P max ) W = specimen width (mm) σ u = ultimate strength (MPa) K = stress intensity (MPa √ m) K th = threshold stress intensity (MPa √ m) CT = compact tension specimen HIP = hot isostatic process RHN = Rockwell hardness number SDAS = secondary dendritic arm spacing (μm) I N T R O D U C T I O NFatigue is an important parameter to be considered in the behaviour of mechanical components subjected to constant and variable amplitude loading. Mechanical, metallurgical and environmental variables can influence the fatigue resistance of a structural component. Fatigue is a primary cause of all engineering failure. The increased use of cast aluminium alloys in automotive applications creates the need for a deeper understanding of fatigue performance and the influence of processing parameters. The method of assessing the fatigue properties resulting from Correspondence: H. K. Govindaraju. E-mail: anchith_g_raj@yahoo.co.in different processing conditions require establishment of extensive database of rate of crack growth versus stress intensity (da/dN -K) information.Several authors 1-5 have concentrated on fatigue crack growth (FCG) studies of different aluminium alloys. Various microstructural features such as Si morphology, secondary dendrite arm spacing (DAS) as well as heat treatment, porosity level, testing conditions, operating atmospheres, operating temperature, etc. have been investigated. Si morphology influences on FCG of aluminium alloy, die cast alloys, Al -12% Si -0.35% Mg and rheocast alloys have been reported. Secondary dendritic arm spacing was observed to play an important role in the fatigue behaviour for different heat treating conditions of

Improved fatigue crack growth resistance by retrogression and re‐aging heat treatment in 7010 aluminum alloy

“…It has been shown that various microstructural features such as grain size, precipitates, and PFZ influence the FCGR behavior. 19,45,46 The measured grain sizes in both T6 and RRA-treated alloys were almost similar and about 10 μm. Since both heat treatments, ie, RRA and T6, were carried out following the same solution treatment temperature and low temperature aging, the presence of Al 3 Zr dispersoids (as shown in SAED in Figure 2C) acts as pinning sites on the grain boundaries.…”

“…Hence, intrinsic mechanism of crack growth itself is expected to cause reduction in the growth rates in the RRA‐treated aluminum alloy. It has been shown that various microstructural features such as grain size, precipitates, and PFZ influence the FCGR behavior . The measured grain sizes in both T6 and RRA‐treated alloys were almost similar and about 10 μm.…”