Microstructural evolution under low shear rates during Rheo processing of LM25 alloy

© ASM InternationalMicrostructural features of LM25 alloy processed by two different routes: (1) conventional casting, and(2)shear casting based on inclined heated surface are studied. The microstructures of the primary phase for the shear-cast samples show rosette or ellipsoidal morphologies. Heat transfer of contacting melt with the inclined tube surface and shear stress exerted on the layers of the melt as result of gravitational force are crucial parameters for the microstructural evolution. Compared to those produced by conventional casting, shear-cast samples have a much improved tensile strength and ductility due to globular microstructure

Influence of Semisolid and Strontium Addition on Dry Sliding Wear Behavior of Hypoeutectic Al-Si Alloy

The study aims to investigate the effect of semisolid structure and strontium (Sr) addition on the wear behavior of hypoeutectic Al-Si alloy. Semisolid hypoeutectic Al-Si alloy was prepared using cooling slope casting with addition of 0 to 0.93 wt.% Sr. Microstructural study was done using an optical microscope. Vicker microhardness and pin on disc tribometer were used for microhardness and wear testing. When compared to conventional casting, the microhardness of the semisolid hypoeutectic Al-Si alloy improved by 9.8%. Sr addition at 0.43 wt.% resulted in a refined eutectic structure with a 17% increase in hardness over conventional casting. The globular structure α-Al formed during semisolid casting reduced porosity, and the addition of Sr refined the eutectic silicon into a fine fibrous structure that is tightly bound with the Al matrix. These are the primary factors that contribute to the high wear resistance in modified-Sr semisolid alloys

Effects of processing parameters on microstructure evolution of Al-7Si-Mg alloy by cooling slope casting

This work investigates the effects of pouring temperature, slope length, and slope temperature in cooling slope casting on the formation of globular microstructure of Al-7Si-Mg alloy. The remnant alloy on the slope during casting was quenched and characterized at different stages of flow to evaluate the microstructure features developed in cooling slope casting. The primary alpha-Al dendritic phase found in conventional cast alloy was transformed into globular shape in slope-processed cast alloy. Finer and more homogenous primary alpha-Al phase was formed at lower pouring temperature (625 degrees C). The effect of slope length on microstructure of Al-7Si-Mg alloy was significant at high pouring temperatures (640 and 660 degrees C) but was not visible at low pouring temperature (625 degrees C). The microstructure of alloy became coarser with increasing slope temperature

Dry wear behavior of cooling-slope-cast hypoeutectic aluminum alloy

This study investigated the effect of use of a cooling slope on the microstructure, hardness and wear behavior of Al-7Si-Mg alloy. The Al-7Si-Mg alloy was cast with and without a cooling slope at a pouring temperature of 640 degrees C. Examination with optical and electron microscopes showed that the microstructure of cast samples using the cooling slope comprised fine and globular primary alpha-Al phase with homogeneous distribution of eutectic phase, while conventionally cast samples featured coarse and dendritic primary alpha-Al phase. The wear resistance of the cast sample was significantly better with cooling slope casting. The wear mechanism was found to be a combination of adhesion, delamination, oxidation and abrasive wear for both cooling slope- and conventionally cast samples. The wear mechanisms of cast samples both with and without cooling slope are similar and follow Archard's law. The cooling slope-cast samples with fine and globular alpha-Al phase, high hardness and low specific wear rate (K') showed the highest wear resistance of 10.08 x 10(-5) mm(3) N-1 m(-1)

Microstructural evolution and wear characteristics of equal channel angular pressing processed semi-solid-cast hypoeutectic aluminum alloys

This work investigated the microstructural evolution of Al-7Si-Mg alloy cast semi-solid using a cooling slope as well as conventional casting followed by equal channel angular pressing (ECAP) in a 120 degrees die. Feed materials were prepared for ECAP by cooling slope casting and by conventional casting. The microstructure of the processed alloys extruded was observed by optical microscope and by transmission electron microscope, and their hardness and wear resistance were evaluated. After ECAP processing, the primary alpha-Al phase tended to be elongated while the Si particles became fragmented and more nearly globular in shape and uniform in size than in the as-cast sample. The microstructure of the cooling slope-cast ECAPed samples was more homogenous than that of the conventionally cast ECAPed sample. The alpha-Al phase sub-grains were refined to sub-micrometer sizes for samples cast by both methods after ECAP. The hardness of the cooling slope-cast ECAPed sample was also higher than that of the conventionally cast ECAPed sample. The wear resistance of the alloy improved after cooling slope casting and ECAP processing. (C) 2014 The Authors. Published by Elsevier Ltd

The Influence of Hydroxyapatite and Alumina Particles on the Mechanical Properties and Corrosion Behavior of Mg-Zn Hybrid Composites for Implants

Considering the necessity for a biodegradable implant alloy with good biocompatibility and mechanical strength, dual ceramic particles of HAP and Al2O3 were added to Mg-Zn alloy to produce a new hybrid composite using powder metallurgy. The paper reports the mechanical and corrosion behaviour of Mg-Zn/HAP/Al2O3 hybrid composites containing variable wt.% HAP and Al2O3 with 15 wt.% total ceramic content. The powders of Mg, Zn, Al2O3 and HAP were milled in a high-energy ball mill, and then compacted under 400 MPa and sintered at 300 °C. Density and compression strength increased with increasing Al2O3 content. HAP facilitated weight gain in Hanks balanced salt solution due to deposition of an apatite layer which promoted anodic behaviour with higher corrosion resistance. A hybrid composite of Mg alloy with 5 wt.% Al2O3 and 10 wt.% HAP displayed 153 MPa compressive strength, 1.37 mm/year corrosion resistance and bioactivity with a CA:P ratio of 1:1.55 and appears to be the most promising biodegradable implant material tested

Microstructure-property relationship for friction stir processed magnesium alloy

Friction stir processing (FSP) of Mg based AE42 alloy was performed under single pass as well as double pass conditions. The evolution of microstructure was investigated using electron back scatter diffraction (EBSD) analysis. EBSD revealed that the grain size and texture varies within the nugget zone of friction stir processed region. The variation of mechanical properties across the nugget region was evaluated using nanoindentation. Hardness and Young's modulus was found to increase along the depth of the friction stir processed specimen. This was attributed to a finer grain structure with increasing depth. The friction stir processed specimen showed higher tendency toward strain hardening compared to as-cast alloy. Understanding microstructure–property relationship paves the way for optimization of FSP conditions and development of advanced functional Mg alloys