Deformation behavior of an A356 alloy containing small sub-grains with wide low-angle boundary

Abstract

We introduce a new method for overcoming the strength–ductility trade-off by using a non-metallic alloying method, whereby numerous oxygen atoms are introduced in a conventional A356 alloy (I-A356 alloy). Self-organized nanofibers containing oxygen atoms formed in the melt had a chemically coherent interface with the matrix after solidification. Furthermore, the nanofibers (~10 nm in width) developed small sub-grains (<1 μm in size) with wide low-angle boundaries within the grains. Pre-existing dislocations developed by the small lattice mismatch between the nanofibers and matrix promoted strong activities. The sub-grain boundaries do the role of dislocation cells during plastic deformation, imparting high elongation to the I-A356 alloy. In addition, finely dispersed Si-rich nanoprecipitates formed during the aging treatment. The oxygen-rich intermixed layer at the Al–Si interfaces with a small radius of curvature drove Al–Si interdiffusion owing to the high attractive binding energy with Al. Thus, in addition to Mg2Si precipitates, the Si-rich nanoprecipitates further enhanced the alloy strength. Therefore, both, the ultimate tensile strength and elongation to failure of the I-A356 alloy, significantly increased by approximately 69.6 MPa and 14.8%, respectively, in relation to those of the A356 alloy.