Hardening (metallurgy)

About: Hardening (metallurgy) is a research topic. Over the lifetime, 25584 publications have been published within this topic receiving 376012 citations.

Microstructure, tensile and fatigue properties of AA6061/20 vol.%Al2O3p friction stir welded joints

Abstract: Metal matrix composites reinforced with Al 2 O 3 particles combine the matrix properties with those of the ceramic reinforcement, leading to higher stiffness and superior thermal stability with respect to the corresponding unreinforced alloys. However, their wide application as structural materials needs proper development of a suitable joining processes. The present work describes the results obtained from microstructural (optical and scanning electron microscopy) and mechanical evaluation (hardness, tensile and low-cycle fatigue tests) of an aluminium alloy (AA6061) matrix composite reinforced with 20 vol.% fraction of Al 2 O 3 particles (W6A20A), welded using the friction stir welding process. The mechanical response of the FSW composite was compared with that of the base material and the results were discussed in the light of microstructural modifications induced by the FSW process on the aluminium alloy matrix and on the ceramic reinforcement. The FSW reduced the size of both particles reinforcement and aluminium grains and also led to overaging of the matrix alloys due to the frictional heating during welding. The FSW specimens, tested without any post-weld heat treatment or surface modification showed lower tensile strength and higher elongation to failure respect to the base material. The low-cycle fatigue life of the FSW composite was always lower than that of the base material, mainly at the lower strain-amplitude value. The cyclic stress response curves of the FSW composite showed evidence of progressive hardening to failure, at all cyclic strain-amplitudes, while the base material showed a progressive softening.

Optimization of hardening of Al–Zr–Sc cast alloys

Abstract: The effects of composition, cooling rate after the end of solidification, and annealing regime on the structure and hardening of binary and ternary alloys of the Al–Sc–Zr system are studied. The liquidus in Al–Sc–Zr alloys is experimentally assessed in order to facilitate the correct choice of casting temperatures. The precipitation during slow cooling after the end of solidification causes hardening in the as-cast state and decreases the hardening effect during annealing. It is shown that the full hardening ability of precipitates can be achieved only upon their homogeneous distribution in the matrix. The optimum total concentration of Sc and Zr in aluminium alloys should be about 0.3 wt% at the ratio Zr:Sc ≥ 2. That allows conventional casting temperatures and considerable hardening during annealing.

Heat of hydration in concrete

Abstract: Summary The paper traces the development of a function between time and temperature, which makes it possible to refer the process of hardening of concrete at varying temperature to hardening at constant temperature. It is further shown that it is possible to predetermine the temperature of concrete during hardening when properties of concrete, sizes and shape of the specimen, insulation and external temperature are known. The time temperature function can also be applied to the development of strength. The validity of the theory is demonstrated by the results of tests upon 27 American and 3 Danish cements.