Morphological analysis of SSM Al-4.5wt.% Cu measured by the rheocast quality index
Abstract There is a direct relationship between grain size obtained from macrostructure characterisation and the globule size and shape factor, obtained from microstructure characterisation: the smaller the grain size, the smaller the globule size and shape factor. Due to this a rheocast quality index ( RQI = globule size /( grain size × shape factor) ) was used to evaluate the Al–4.5 wt.% Cu alloy produced by strain induced melting activation (SIMA). The structure that presents the smallest grain size, the smallest shape factor, and the most homogeneous and globular size of the primary phase, has the best RQI and consequently the best behaviour in the semi-solid forming. Four different as-cast structures were cold rolled to obtain 20 and 40% deformation and were partially melted at 635 °C at holding times of 5 min. Both, macro- and microstructure were characterised.
Mechanical Properties and Microstructure Improvement of a Two-Step Strain Induced Melt Activation Processed 7075 Aluminum Alloy Compared to that SIMA Process
Strain induced melt activation process (SIMA) creates a globular microstructure which improves the hardness and ultimate tensile stress (UTS) of 7075 aluminum alloys. But, at the grain boundaries of SIMA processed 7075 aluminum alloy, presence of continuous and brittle intermetallic compounds and the eutectic structure result in decreasing mechanical properties, such as elongation, formability and etc. Hence, in order to improve microstructure and formability of 7075 aluminum alloy respect to SIMA process, a new process was done that is called two-step strain induced melt activation (TSSIMA). This process, which has been mentioned in the experimental procedure section, both organized globular structure and significantly modified the microstructure of the alloy compared to that of the SIMA method. It promoted discontinuity and more homogeneity in distribution of the precipitates and, approximately removed the eutectic mixture. Performing the rolling process on the alloy also revealed that it is more effective in formability enhancement in comparison with SIMA process. Also, it increased the hardness of 7075 aluminum alloy respect to that of SIMA process.
Particle growth by coalescence during liquid phase sintering of Fe-Cu
Abstract Particle growth during liquid phase sintering of Fe-30 wt% Cu and Fe-60 wt% Cu was measured and compared with a recently developed coalescence theory. Measured normalized particle size distribution, time-dependence of average particle size and dependence of growth rate on solid phase volume fraction agree well with calculations based on the assumption of a diffusion-controlled coalescence process where all component particles are assumed to have equal coalescence frequency. Slight discrepancies can be explained as the results of nonspherical particle shape and of favored coalescence opportunity for larger particles.