Strain path and microstructure evolution during severe deformation processing of an as-cast hypoeutectic Al–Si alloy

Abstract

Microstructure evolution in an as-cast Na modified Al-7%Si (wt. pct.) alloy was examined during redundant and monotonic straining by repetitive equichannel angular pressing (ECAP) under ambient temperature conditions, and during friction stir processing (FSP). Redundant straining during repetitive ECAP was accomplished by processing following route B C while monotonic straining employed route A. Single-and multi-pass FSP was conducted on this same as-cast material using an FSP tool having a threaded pin. The as-cast microstructure comprises equiaxed primary a dendrite cells embedded in the Al-Si eutectic constituent. The evolution of this microstructure during repetitive ECAP can be described by idealized models of this process. The primary and eutectic constituents can still be discerned and the Si particle distribution is not homogenized even during ambient temperature processing involving von Mises strains [9.0. In contrast, the primary and eutectic constituents cannot be distinguished in the stir zone after even a single FSP pass. Strain estimates based on the shape change of the primary a constituent indicate that the Si particle distribution has become homogeneous at local von Mises strains of 2.5-3.0 during the FSP thermomechanical cycle. Mechanical property data are consistent with strain path during SPD processing by repetitive ECAP and FSP.

The Effect of Concurrent Straining on Phase Transformations in NiAl Bronze During the Friction Stir Processing Thermomechanical Cycle

“…Si alloy after FSP. [28] This article will report on an investigation into the estimation of strain from distortion of microstructure constituents and also show that concurrent deformation accelerates the rate of dissolution of the eutectoid constituent upon heating during FSP of an NiAl bronze material.…”

A critical examination of the paradox of strength and ductility in ultrafine-grained metals

“…Thus, these alloys are well documented and there is a good database that may be used for a comparison of results using different processing techniques. Some limited results are available on the effect of processing by ECAP 33,34 and HPT 35-38 on cast Al-Si alloys but there are no systematic reports on the evolution in strength and ductility as a function of the imposed strain in HPT and the processing temperature. Thus, a conclusive processing route for achieving high ductility and high strength in Al-Si alloys has proven elusive.…”

Influence of microstructural stability on the creep mechanism of Al–7wt% Si alloy processed by equal channel angular pressing

“…2a-d). Although ECAP route A does not achieve a complete redistribution as it is obtained with FSP [24,25] and HPT [26,27], the mechanical properties are considerably improved with respect to the as-cast alloy. Additionally, from the first ECAP pass a fine (sub)grain microstructure, $ 250 nm, is formed.…”