Dynamic Grain Growth in a Non-Superplastic Al-6Ni Alloy

摘要

An Al-6Ni alloy was deformed and annealed to the Zener limit to produce a relatively uniform equiaxed grain structure. It was then uniaxially deformed at 500℃ to various strains, at different strain rates. The strain rate sensitivity (m) of the alloy was measured, and confirmed that despite the fine grain size, it was not superplastic. The microstructure was studied in detail and was shown to dynamically coarsen with increasing strain at all strain rates studied, something which is usually specifically associated with superplastic alloys. This is ascribed to dynamic grain growth being a result of the geometric deformation destabilising the pinning pressure that particles were able to apply to the grain boundary. Thus, dynamic grain growth is to be expected from any fine grained, Zener pinned alloy that undergoes deformation where the grain boundary mobility is comparable to the rate of deformation. This implies that dynamic microstructural coarsening may not be a resulting consequence of superplasticity, but is simply a phenomenon that many superplastic alloys demonstrate through having fine grained, Zener pinned microstructures.