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The stability of Al foams during processing is crucial to producing uniform Al foams. Once pores form during processing, no matter which conventional methods are used, the pores grow and/or merge into large ones, which could cause Al foams to “collapse”. Therefore, it has attracted great attention of researchers to enhance the stability of Al foams during processing for improved quality of Al foams. A novel approach to produce Al-alloy foams, “Rheofoaming”, is presented in this paper. A twin-screw rheomixer fitted with a gas inlet near the end cap is used in this work. The mechanism of this approach is firstly to increase the viscosity of semisolid slurry of Al alloy by adding sub-micron Al2O3 particles and then to mix N2 gas with the semisolid slurry using a twin-screw rheomixer, which can offer high shear rate and intensive turbulence. The gas pores in the semisolid slurry are stretched and broken into smaller ones in the rheomixer. Al foams are very stable during the processing due to small pore sizes and high viscosity of semisolid slurry. The microstructure of rheofoamed Al foams and the process of this new approach have been described in this paper. [ABSTRACT FROM AUTHOR]

In order to develop aluminium–zinc-based a new alloy for tribological applications, six binary Al–Zn and seven ternary Al–25Zn–(1–5)Cu were prepared by permanent mould casting. Their microstructure and mechanical properties were investigated. Dry sliding friction and wear properties of the ternary alloys were investigated using a pin-on-disc machine. Surface and subsurface regions of the wear samples were studied with scanning electron microscopy (SEM). The highest hardness and tensile strength were obtained with the Al–25Zn alloy among the binary ones. The microstructure of this alloy consisted of aluminium-rich α and eutectoid α + η phases. Addition of copper to this alloy resulted in the formation of θ (CuAl2) phase. The hardness of the ternary alloys increased with increasing copper content. The highest tensile and compressive strengths and wear resistance and the lowest friction coefficient were obtained from the ternary Al–25Zn–3Cu alloy. The dimensional change measured on ageing (stabilization) of this alloy was found to be much lower than that obtained from the copper containing zinc-based alloys. Microstructural changes were observed below the surface of the wear samples of the Al–25Zn–3Cu alloy. These changes were related to the heavy deformation of the surface material due to normal and frictional forces, and smearing and oxidation of wear material. Adhesion was found to be the main wear mechanism for the alloys tested. [ABSTRACT FROM AUTHOR]

The addition of Sr in Al-Si alloys as a modifier causes a transition of the morphology of eutectic silicon from coarse plate-like or acicular to fine fibrous. However, it may also lead to the formation of long columnar dendritic α-Al phase. Al-5Ti-1B master alloy is often used as a grain refiner to achieve the fine equaixed grains in aluminum and aluminum alloys. The aim of the present study is to highlight the effect of Al-5Ti-1B master alloy additions on the microstructure of near-eutectic Al-Si alloys modified with Sr. When the addition of Al-5Ti-1B master alloy was below 0.82 mass%, the dendritic α-Al phase changed from long columnar to equiaxed, and there were no noticeable changes of the morphology and size of eutectic silicon, while the size of eutectic cells decreased slightly. However, when the addition was above 0.82 mass%, the deleterious influence of Al-5Ti-1B master alloy on the modification effect of Sr emerged and with further increases in addition level a fully unmodified microstructure was finally produced. The results indicate that the effective Sr in the melt decreases with increased addition of Al-5Ti-1B. The poisoning event of Al-5Ti-1B master alloy on the modification of Sr is supposed to be related with the interaction between Sr and Ti. [ABSTRACT FROM AUTHOR]

The friction-stir welding of a 62 Be-38 Al composite consisting of a Be phase in a continuous Al matrix produced a recrystallized, refined weld zone microstructure with intermixed, equiaxed grains of Be and Al, which increased in hardness by 43 percent from the base metal hardness. Like other friction-stir weld processes, there was no melting and no apparent release of airborne Be or BeO, rendering the process environmentally and technically attractive. [ABSTRACT FROM AUTHOR]

This article presents information on deformation of fracture behavior of an aluminum and lithium alloy 8090. The effect of microstructure on the deformation mode and fracture behavior of age-hardened alloys has been the topic of many investigations. The deformation behavior could be modified by varying the aging condition. In the underaged condition, precipitate shearing tends to lead to an inhomogeneous distribution of slip, whereas, in the overaged condition, precipitate bypass by dislocations tends to homogenize the slip distribution.