Superplasticity and superplastic forming of aluminum metal-matrix composites

Abstract

Editor's Note: This article describes the composition of metal·matrix composites using a nomenclature system consisting of five parts: the matrix alloy designation, the reinforcement material, the volume percent of the reinforcement, the morphology of the reinforcement, and the generic temper designation. Under this system, a matrix of aluminum alloy 6061 reinforced with 40 vol. % SiC particulate and given a T6 heat treatment is written as 6061 /SiC/ 4Op-T6. When a matrix/reinforcement system is being discussed in general terms, it is deSignated in the same fashion, but a subscript is affixed to the reinforcement material designation to indicate whether it is whisker (w) or particulate (p). Thus, the family of composites formed by reinforcing aluminum alloy 2124 with Si,N. whiskers is designated 2124/Si,N«wl' Superplasticity hos been observed in many aluminum metal-matrix composites at extremely high strain rates (approximately 0.1-1 S-I). These materials generally exhibited a strain-rate sensitivity value of about 0.3 and a maximum elongation of about 300%. It is believed thot the presence ofa liquid phose, or in some cases a low-melting-point region, at the reinforcement/matrix interfaces is responsible for the phenomenon. This phenomenon is not observed in all reinforced composites, despite the fact thot they contain fine grain sizes. Thus, a fine matrix grain size is a necessary but insufficient condition for the high-strain-rate superplasticity.

Superplastic deformation characteristics and constitution equation in rapidly solidified Mg–Al–Ga alloy

“…At a strain rate of 1 s -1 , a tensile specimen may undergo the adiabatic heating significantly during the deformation, and then strain softening behavior caused by raising the temperature of the specimen may occur. [20][21][22] It was reported that high strain rate superplasticity in aluminum metal-matrix composites occurs in the presence of some liquid, even though the temperature appears to be below the solidus. 22 Because of the high strain rate, the effective temperature is expected to be higher than nominal testing temperature, due to adiabatic heating.…”

“…[20][21][22] It was reported that high strain rate superplasticity in aluminum metal-matrix composites occurs in the presence of some liquid, even though the temperature appears to be below the solidus. 22 Because of the high strain rate, the effective temperature is expected to be higher than nominal testing temperature, due to adiabatic heating. Then the effective temperature rises above the solidus line.…”

Temperature dependence of threshold stress for aluminum-based materials exhibiting high strain rate superplasticity

“…Nieh et. al proposed that incipient melting at grain boundaries makes HSRS possible in the 2124-SIC composite [4,5,15], and this idea has been adapted by various workers [7,9,10]. Bieler et al analyzed HSRS of the IN90211 aluminum alloy assuming that a threshold stress resists dislocation motion needed to accommodate grain boundary sliding, and many experimental data of HSRS could be properly interpreted by incorporating threshold stress [18,21].…”

Liquid phase densification of Al-4.5wt.% Cu powder reinforced with 5wt.% Saffil short fibers during hot pressing

“…The value n = 1 represents a viscous flow process [15] and n = 2 is found for the case of superplastic deformation [16]. The case of n = 3 applies to the viscous glide mechanism [17].…”