The control of a microstructure, during and after hot forming, is crucial to tailor optimum mechanical properties for specific applications. Recrystallization is a key process which may contribute to a great extent to microstructure development. Dynamic recrystallization is becoming an attracting research area to investigate novel hot forming routes in order to maximize the performance of aluminum products while shortening the time required for manufacturing. A continuous dynamic recrystallization (CDRX) mathematical model was developed by Gourdet-Montheillet (GM) to predict the inherent phenomena of an AA1200 alloy. In the present work, the original GM model has been extended and applied to study CDRX in a 5052 aluminum alloy. The proposed model embodies a solid solution and second phase strengthening, through newly estimated kinetic factors and a kinetic constant, respectively, to discern the CDRX behavior of 5052 aluminum alloy compared to AA1200. The latter kinetic constant relies on the Kocks-Mecking-Estrin (KME) theory. The input law of the fraction of high angle boundaries (f HAB ), as a function of strain (e) (but independent of temperature and strain rate), is defined as the best fitting function of the experimental data. The results are presented in terms of stress-strain curves, dislocation density, and (sub) grain size, as these are important design parameters from an industrial and engineering viewpoint. The model has been validated successfully, from both a qualitative and quantitative point of view, against various literature data sources and tests (e.g., hot compression, hot plane strain compression, and equal channel angular pressing) pertaining to the 5052 alloy and other similar Al-Mg alloys.

The welding of cemented carbide to tool steel is a challenging task, of scientific and industrial relevance, as it combines the high level of hardness of cemented carbide with the high level of fracture toughness of steel, while reducing the shaping cost and extending the application versatility, as its tribological, toughness, thermal and chemical properties can be optimally harmonised. The already existing joining technologies often impart either insufficient toughness or poor high-temperature strength to a joint to withstand the ever-increasing severe service condition demands. In this paper, a novel capacitor discharge welding (CDW) process is investigated for the case of a butt-joint between a tungsten carbide-cobalt (WC-Co) composite rod and an AISI M35 high-speed steel (HSS) rod. The latter was shaped with a conical-ended projection to promote a high current concentration and heat at the welding zone. CDW functions by combining a direct current (DC) electric current pulse and external uniaxial pressure after a preloading step, in which only uniaxial pressure is applied. The relatively high heating and cooling rates promote a thin layer of a characteristic ultrafine microstructure that combines high strength and toughness. Morphological analysis showed that the CDW process: (a) forms a sound and net shaped joint, (b) preserves the sub-micrometric grain structure of the original WC-Co composite base materials, via a transitional layer, (c) refines the microstructure of the original martensite of the HSS base material, and (d) results in an improved corrosion resistance across a 1-mm thick layer near the weld interface on the steel side. A nano-indentation test survey determined: (e) no hardness deterioration on the HSS side of the weld zone, although (f) a slight decrease in hardness was observed across the transitional layer on the composite side. Furthermore, (g) an indication of toughness of the joint was perceived as the size of the crack induced by processing the residual stress after sample preparation was unaltered.

Tungsten carbide-cobalt (WC-Co) composites are a class of advanced materials that have unique properties, such as wear resistance, hardness, strength, fracture-toughness and both high temperature and chemical stability. It is well known that the local indentation properties (i.e., nano- and micro-hardness) of the single crystal WC particles dispersed in such composite materials are highly anisotropic. In this paper, the nanoindentation response of the WC grains of a compact, full-density, sintered WC-10Co composite material has been investigated as a function of the crystal orientation. Our nanoindentation survey has shown that the nanohardness was distributed according to a bimodal function. This function was post-processed using the unique features of the finite mixture modelling theory. The combination of electron backscattered diffraction (EBSD) and statistical analysis has made it possible to identify the orientation of the WC crystal and the distinct association of the inherent nanoindentation properties, even for a small set (67) of nanoindentations. The proposed approach has proved to be faster than the already existing ones and just as reliable, and it has confirmed the previous findings concerning the relationship between crystal orientation and indentation properties, but with a significant reduction of the experimental data.