Papers by Author: Bradley J. Diak

Abstract: A novel experimental investigation of both high and medium stacking fault energy bi-crystals of aluminum and copper, respectively, show that orientation, grain interaction and material are all key factors in the stability of some ideal rolling texture components. Ideal {110} or {112} orientations obtained from high purity aluminum or copper single crystals were embedded within a {110} crystal orientation of the same material and reduced 60 percent by channel die compression at room temperature. Spatial misorientations developed inside the deformation bands were analyzed using SEM-based EBSD. The presence of long-range orientation gradients in some of the crystals revealed the interacting nature of polycrystalline deformation. From the results it is proposed that f.c.c. polycrystalline grains can be classified according to their stability and susceptibility to deformation: (i) stable and interacting; (ii) unstable and interacting; (iii) stable and non-interacting; (iv) unstable and non-interacting.

Abstract: Magnesium (Mg) is a hexagonal close-packed light metal whose deformation re-sponse is characterized predominantly by easy slip on the f0002g basal plane at temperaturesbelow 200°C. Rolled sheet products develop a strong basal texture and become \plasticallychallenged" in subsequent forming operations. In the literature, additions of rare earth ele-ments (REE) to Mg have inconsistently reported non-basal texture formation. In this work,Mg-0.2wt%Gd and 0.2-wt%La were investigated to determine whether the presence of theseelements contributed to non-basal texture formation after elevated temperature plane straincompression. Test specimens were prepared from book-mould castings after homogenization at400°C, and reduced 50% in a channel die at 250, 325, or 375°C and 10^-2/s. The stress-strainbehaviours were all characterized by apparent twin-related softening, followed by monotonichardening to the end of the imposed deformation. The yield stress for Mg-0.2%La (15-22 MPa)was higher and less temperature dependent than for Mg-0.2%Gd (10-18 MPa). Texture mea-surements indicate the spread of ideal basal texture about TD with increased temperature, butalso also greater non-basal textures in the Mg-0.2%Gd alloy, particularly at 325°C. Electronchanneling contrast imaging revealed a more re ned and homogeneous substructure in the Gd-containing alloy compared with larger microbands in the La-containing alloy, and suggests thatcontinuous recovery and other available slip systems may contribute to these di erences.

Abstract: This study examines the recovery behaviour of the inter-alloy region between a core AA6XXX clad with AA3003 after 72% rolling reduction. Sample coupons were heated isochronally or isothermally, at different temperatures or times, respectively, to probe the recovery kinetics of x-ray peak broadening, x-ray macro-texture, and micro-hardness from the cold rolled state. The inter-alloy region had a strong β-fibre typical of rolled Al. The recovery of the {220} and {311} x-ray line profiles were observed between anneals. The full width half maximum was determined from a pseudo-Voigt fit of the profiles to obtain the defect-related information. Distinct changes in the peak shape and microhardness were observed above 80°C (start of recovery), which goes on all the way to 300°C due to recovery, and beyond 300°C both hardness and peak width drop rapidly (recrystallization start), the latter behaviour being closer to AA3004. Modified Williamson-Hall analysis confirms that recovery is due to dislocation annihilation.