Processing of aluminum-graphite particulate metal matrix composites by advanced shear technology

Copyright @ 2009 ASM International. This paper was published in Journal of Materials Engineering and Performance 18(9) and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.To extend the possibilities of using aluminum/graphite composites as structural materials, a novel process is developed. The conventional methods often produce agglomerated structures exhibiting lower strength and ductility. To overcome the cohesive force of the agglomerates, a melt conditioned high-pressure die casting (MC-HPDC) process innovatively adapts the well-established, high-shear dispersive mixing action of a twin screw mechanism. The distribution of particles and properties of composites are quantitatively evaluated. The adopted rheo process significantly improved the distribution of the reinforcement in the matrix with a strong interfacial bond between the two. A good combination of improved ultimate tensile strength (UTS) and tensile elongation (e) is obtained compared with composites produced by conventional processes.EPSR

The Bauschinger effect in a SiC/Al composite

SiC/Al composites have interesting mechanical properties, the tensile yield stress, whereas, the apparent modulus in tension is greater than that in compression. The Bauschinger effect of SiC/Al composites is also asymmetric with regard to loading directions. Quantitative measurements of the asymmetry of composite Bauschinger Effect was made in this research . An investigation was undertaken to determine the origin of the asymmetrical Bauschinger effect. We have successfully reconstructed the observed asymmetry using an internal stress model based on the development of internal stresses, conveniently referred to as the ``black stress``, and work hardening

Mechanism for Grain Refinement and Mechanical Properties of AZ91 Mg Alloy by Carbon Inoculation

AbstractThe effect of charcoal on the grain refinement and mechanical properties of the AZ91 is investigated in the present study. The results show addition of 0.4 wt% charcoal produced maximum grain refinement in the AZ91 Mg alloy by reducing the grain size from 100 to 14μm. Such fine grain structure achieved through addition of charcoal suggests that the Al4C3 and Al2MgC2 particles formed in the melt have acted as efficient nucleating sites during solidification of α-Mg. Significant improvement in mechanical properties observed with charcoal addition is attributed to the grain refinement and the presence of fine carbide particles

Modeling of the Effect of a Defect on HCF Life of a Magnesium AZ91 Specimen Subjected to Transverse Load

AbstractMaterial defects formed while manufacturing, fabricating and material handling are crucial in deciding the fatigue life of machine member. Research reports the modelings of effect of a defect upon the high cycle fatigue (HCF) behavior of materials are sparse. This paper attempts to model the effect of a defect over the HCF life of cast magnesium AZ91alloy by introducing defects of two different volumes, at three different locations (top, middle and bottom of the specimen in critical zone) in AZ91 specimen, which is subjected to transverse load. Transverse load HCF test results obtained using ASTM standard D671 specimens machined from low pressure cast and gravity cast magnesium AZ91 were used for the modeling. The results reveals that defect in the critically stressed part of the specimen drastically reduce fatigue life of specimen even for an insignificant increment of load

Investigation on mechanical properties and creep behavior of stir cast AZ91-SiCp composites

The room temperature mechanical properties and high temperature creep behavior of AZ91 alloy reinforced with SiCp synthesized via stir casting have been evaluated. The mechanical properties showed improvement with respect to the amount of reinforcement content. The creep testing of the composites carried out at a temperature of 175 °C under constant stress of 80, 100 and 120 MPa reveals different creep characteristics depending upon the reinforcement content and the applied load. The true stress exponents of different composites calculated from minimum creep rate indicate the possible mechanisms of creep deformation