Journal of Light Metals最新文献

The principle that alloys are designed to accommodate the manufacture of goods made from them as much as the properties required of them in service has not been widely applied to pressed and sintered P/M aluminium alloys. Most commercial alloys made from mixed elemental blends are identical to standard wrought alloys. Here we use a statistical design of experiment approach to re-evaluate the composition spectrum of the 2xxx alloys. Copper has the major influence on the tensile properties. Magnesium and silicon do effect some properties, but to a lesser extent. The major value of magnesium is breaking up the surface oxide layer. Conversely, an extensive secondary pore network develops from excess magnesium and this severely limits the ductility. Hard intermetallic particles, which are a residue of the sintering liquid, also reduce the tensile ductility. The tensile strength is limited by the low ductility, which is related to the equilibrium liquid volume at the sintering temperature, as well as the sintered density.

A novel, low-cost sinter-forging approach to processing particle reinforced metal matrix composites for high-performance applications was examined. The microstructure of the sinter-forged composites exhibited relatively uniform distribution of SiC particles, which appeared to be somewhat aligned perpendicular to the forging direction. The degree of alignment and interparticle bond strength was not as high as that observed for the extruded composite. The sinter-forged composite exhibited higher Young’s modulus and ultimate tensile strength than the extruded material, but lower strain-to-failure. The higher modulus and strength were attributed to the absence of any significant processing-induced particle fracture, while the lower strain-to-failure was caused by poorer matrix interparticle bonding compared to the extruded material. Fatigue behavior of sinter-forged composites was similar to that of the extruded material. Fe-rich inclusions were extremely detrimental to fatigue life. Cleaner processing, which eliminated the inclusions, enhanced the fatigue life of the sinter-forged composites to levels similar to that of the extruded material.

AlYNi amorphous alloys with high mechanical strength and good bending ductility have been produced by rapid solidification technique. Vickers hardness (H_v), Young’s modulus (E) and tensile fracture strength (σ_f) for the amorphous single phase are in the range 365–385 DPN, 71.5–82.2 GPa and 920–1150 MPA, respectively. The crystallized structure of the amorphous alloys consists of coexistent amorphous and fcc-Al phase with a particle size of 5–25 nm. The hardness and tensile fracture strength of these amorphous alloys containing the nanoscale Al particles increase to 550 DPN and 1450 MPA respectively, annealed at 400–550 K for 30 min. This increase in (H_v) and σ_f is considered because the defect-free nanoscale fcc-Al particles homogeneously dispersed in the amorphous matrix effectively resist against shear deformation of the amorphous matrix. This paper describes in detail the effects of annealing temperature on microstructure and mechanical properties of AlYNi amorphous alloys.

It is commonly known that eutectic silicon spheroidizes during a T6 solution heat treatment in Al–Si cast alloys. This spheroidization of the brittle silicon is the main reason for the good fracture elongation values in peak hardened T6 condition. As the silicon spheroidization is known as a side effect of common T6 treatment, there is little known about the influence of sole silicon spheroidization on the mechanical properties. The following paper presents fundamental aspects of the spheroidization process of eutectic silicon in Al–Si cast alloys. It is theoretically as well as experimentally found that the disintegration and spheroidization of well modified eutectic silicon is finished within minutes of exposure to temperatures above 500 °C. The application of this new silicon spheroidization treatment (SST) to thixoformed components results in outstanding fracture elongation values (up to 18%) at good yield strength level (∼230 MPa). FEM simulations of the short high temperature heat treatment confirm a short process time for successful SST even for components with notably variable wall thicknesses.