Low-cycle fatigue behavior of two magnesium alloys

Abstract

Magnesium alloys possess many excellent performances, such as low density, high specific strength, excellent thermal conductivity, and machinability. Magnesium alloys, including Mg-Al alloy family, are increasingly considered for structural components, especially in automotive industry. AZ91 alloy with about 9 wt.% Al and 1 wt.% Zn is the most common magnesium die-casting alloy. It has excellent castability and good room-temperature mechanical properties. AE42 alloy with about 4 wt.% Al and 2.5 wt.% rare earth elements shows good creep resistance to 150 ◦C, and is often used for automotive engine components. For both AZ91 and AE42 alloys, few low-cycle fatigue data are available even though their monotonic tensile and creep properties have been well documented [1–6]. In this paper, the low-cycle fatigue behavior of two magnesium alloys including AZ91 and AE42 were investigated. The rectangular fatigue samples with dimensions 14 × 5 × 5 mm in gauge section were directly machined from die-cast plate of each alloy (designated F). Some fatigue samples were subjected to solution treatment in argon at 415 ◦C for 12 hr (designated T4). Fully-reversed pull-push fatigue tests were performed at room temperature in laboratory air under total strain amplitude control mode using Shimadzu servohydraulic testing machine. All tests were run to final separation of sample, and the corresponding cycling number was defined as low-cycle fatigue life. The fatigue life data (total strain amplitude, et/2, versus number of cycles to failure, Nf) of two alloys with F and T4 status are shown in Fig. 1a and b, respectively. It can be seen that at most of total strain amplitudes except for the lowest strain amplitude of 0.3%, the AZ91-T4 alloy gives greater resistance on strain cycling than the die-cast AZ91 alloy. On the other hand, the AE42 alloy subjected to solution treatment exhibits longer fatigue life than the die-cast AE42 alloy at all total strain amplitudes imposed in this investigation. The above-mentioned fact implies that solution treat-