Effect of temperature on the fatigue cracking mechanisms in A356 Al alloy

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:780

Article

Nelaturu, Phalgun¹  Jana, Saumyadeep²  Mishra, Rajiv S.¹  Grant, Glenn²  Carlson, Blair E.³ 

[1] Univ North Texas, Dept Mat Sci & Engn, Ctr Frict Stir Proc, Denton, TX 76203 USA

[2] Pacific Northwest Natl Lab, Richland, WA 99352 USA

[3] Gen Motors Tech Ctr, Warren, MI 48093 USA

关键词: Fatigue;    Aluminum alloys;    Temperature;    Intergranular cracking;    Transgranular cracking;    Friction stir processing;   

DOI  :  10.1016/j.msea.2020.139175

来源: Elsevier

【 摘 要 】

This work builds on our previous investigation of the room temperature fatigue cracking mechanisms of an A356 Al alloy [1]. Here, we analyze the elevated temperature fatigue cracking mechanisms in cast and friction stir processed (FSP) A356, and contrast them with the room temperature behavior. Two sets of FSP parameters were used to modify the microstructure of the cast alloy. After heat treatment, both the FSPed microstructures exhibited severe abnormal grain growth (AGG) leading to a very wide grain size distribution (from a few microns to a few millimeters). During room temperature fatigue tests, the FSP conditions exhibited significant improvements in fatigue lives, even up to an order of magnitude. However, with increasing temperature, the difference in the performance of the FSPed and Cast microstructures decreased until, at 200 degrees C, all three microstructural conditions exhibited similar fatigue response. Detailed electron back scattered diffraction (EBSD) imaging of failed fatigue specimens was used to study crack behavior. At room temperature, cracks initiated at defect sites or along persistent slip bands (PSBs) and propagated transgranularly. The grain boundaries acted as barriers to crack growth. At elevated temperatures, there was a complete role reversal of the grain boundaries. Cracks initiated along grain boundaries and propagated intergranularly in all microstructures.

【 授权许可】

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