Stress-strain response of a cast 319-T6 aluminum under thermomechanical loading
- PDF / 1,077,860 Bytes
- 13 Pages / 612 x 792 pts (letter) Page_size
- 60 Downloads / 153 Views
I. INTRODUCTION IN recent years, cast aluminum alloys have emerged as alternative materials to cast iron and steels for automotive applications where low weight and good high-temperature performance are required. Although certain studies have been reported on the physical metallurgy and processing of cast aluminum alloys,[5–8] there are only a few studies on the mechanical behavior at high temperatures. This class of materials exhibits properties that depend strongly on local solidification conditions (often represented by secondary dendrite arm spacing (SDAS)) and heat treatment (aging treatment). To ensure the structural integrity of cast aluminum components, it is imperative to establish stress-strain models and life prediction models for these alloys. Since cast components possess a gradient of SDASs (a small SDAS in thin sections and at the surface and a large SDAS in thick sections), it is imperative to develop s –« prediction capabilities over a broad range of SDASs. In the last 20 years, phenomenological constitutive modeling evolved both in the presence of time-independent and time-dependent loading cases. Initially, time-independent models based on yield-surface theory were introduced and utilized.[9,10] To account for creep effects, the classical models have been modified by adding a time-dependent creepstrain component to the time-independent plastic-strain component. This approach has the drawback of not accounting for plastic- and creep-strain interaction. More recently, unified equations have been proposed by Sehitoglu[11] that predict stress relaxation under strain holds, creep strain for
stress hold, and time-dependent metallurgical changes in material structure. Time-dependent changes such as aging and recovery due to temperature holds were described for steels by Sehitoglu and co-workers.[1–4,11] Two-state variables were utilized in these constitutive models, although a single state–variable theory is also capable of representing some of the features of material response.[12] The two state– variable unified model introduced earlier[1–4,11] successfully predicted the stress-strain response of steels and Al 2080 (powder metallurgy) alloys.[13] Further modifications for the case of cast aluminum alloys, due to the unusual amount of cyclic softening and SDAS effects, are undertaken in this work. This alloy family derives its principal strength from u 8 precipitates, which can coarsen and dissolve into the matrix upon exposure to high temperatures, especially under cyclic loading. Before making attempts to develop new constitutive models, extensive experimental results on the stress-strain response of cast aluminum alloys must be obtained. In this study, the stress-strain response of Al 319-T6 alloys with different SDASs was examined under a variety of conditions. Based on these experimental observations, including thermal exposure and cyclic softening effects, the material constants were determined for Al 319-T6. The capabilities of the unified model were checked under isothermal and thermomechanical
Data Loading...
