Mechanical properties of sintered low alloy steels

DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY WITH PRIOR ARRANGEMENT

An examination of the production, heat treatment and mechanical properties of a new wrought magnesium alloy containing 6% Zn. and 1.2% Mn.

DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY AND INFORMATION SERVICES WITH PRIOR ARRANGEMENT

The properties of advanced alumimium alloy systems

2XXX and 7XXX series aluminium alloys have been the accepted materials for airframe construction for many decades. However, only minor improvements in properties have been possible by the development of these alloys since the early 1970's. The constant need to reduce weight in aircraft has therefore led to a resurgence in the research for higher performance aluminium alloys. The reason for this investigation was to evaluate possible alternatives for the existing conventional aluminium alloy 2014 for aircraft wheel applications. Three new technologies in alloy development were considered: a metal matrix composite, an aluminium-lithium alloy and a powder metallurgical alloy. The basic mechanical properties of these advanced materials have already been established to an extent, but their fatigue behaviour has yet to be fully understood. The purpose of this work was to investigate the fatigue properties of the materials concerned, in both air and an aerated 3.5% NaCl solution, and compare these properties to 2014-T6. As well as the basic mechanical properties, fatigue crack propagation data is presented for all of the materials concerned. Additionally, fatigue crack initiation data is presented for the aluminium-lithium alloy and 2014. The D.C. electrical potential method was used to monitor crack growth. Of the materials investigated, the most promising was the aluminium-lithium alloy. However, short transverse properties need to be increased and the commercial cost of the material needs to be decreased before it can be considered as a direct replacement for 2014 for aircraft structural applications. It was considered that the cost of the powder metallurgical alloy would limit its further use. The metal matrix composite material proved to be unsuitable for most ambient temperature applications

Control of soundness and mechanical properties in aluminium-silicon-magnesium alloys

Previously, specifications for mechanical properties of casting alloys were based on separately cast test bars. This practice provided consistently reproducible results; thus, any change in conditions was reflected in changes in the mechanical properties of the test coupons. These test specimens, however, did not necessarily reflect the actual mechanical properties of the castings they were supposed to represent'. Factors such as section thickness and casting configuration affect the solidification rate and soundness of the casting thereby raising or lowering its mechanical properties in comparison with separately cast test specimens. In the work now reported, casting shapes were developed to investigate the variations of section thickness, chemical analysis and heat treatment on the mechanical properties of a high strength Aluminium alloy under varying chilling conditions. In addition, an insight was sought into the behaviour of chills under more practical conditions. Finally, it was demonstrated that additional information could be derived from the radiographs which form an essential part of the quality control of premium quality castings. As a result of the work, it is now possible to select analysis and chilling conditions to optimize the as cast and the heat treated mechanical properties of Aluminum 7% Silicon 0.3% Magnesium alloy.

The mechanical and wear behaviour of B(SiC) fibre-reinforced composite materials

The mechanical properties and wear behaviour of B(SiC) fibre-reinforced metal matrix composites (MMCs) and aluminium alloy (2014) produced by metal infiltration technique were determined. Tensile tests were peliormed at different conditions on both the alloy matrix and its composite, and the tensile fracture surfaces were also examined by Scanning Electron Microscopy (SEM). Dry wear of the composite materials sliding on hardened steel was studied using a pin-on-disc type machine. The effect of fibre orientation on wear rate was studied to provide wear resistance engineering data on the MMCs. Tests were carried out with the wear surface sliding direction set normal, parallel and anti-parallel to the fibre axis. Experiments were perfonned for sliding speeds of 0.6, 1.0 and 1.6 m/s for a load range from 12 N to 60 N. A number of sensitive techniques were used to examine worn surface and debris, i.e: Scanning Electron Microscopy (SEM), Backscattered Electron Microscopy (BSEM) and X-ray Photoelectron Spectroscopy (XPS). Finally, the effect of fibre orientation on the wear rate of the Borsic-reinforced plastic matrix composites (PMCs) produced by hot pressing technique was also investigated under identical test conditions. It was found that the composite had a markedly increased tensile strength compared with the matrix. The wear results also showed that the composite exhibited extremely low wear rates compared to the matrix material and the wear rate increased with increasing sliding speed and normal load. The effect of fibre orientation was marked, the lowest wear rates were obtained by arranging the fibre perpendicular to the sliding surface, while the highest wear was obtained for the parallel orientation. The coefficient of friction was found to be lowest in the parallel orientation than the others. Wear of PMCs were influenced to the greatest extent by these test parameters although similar findings were obtained for both composites. Based on the results of analyses using SEM, BSED and XPS, possible wear mechanisms are suggested to explain the wear of these materials.

Effect of thermal and mechanical processing on tensile properties of powder formed 2124 aluminium and 2124 Al-SiC p metal matrix composite

The aging responses of 2124 Al-SiC p metal matrix composite (MMC) and unreinforced matrix alloy are studied and related to variations in tensile properties. The MMC is aged from Wo starting conditions: (i) stretched and naturally aged and (ii) re-solution treated. Accelerated aging occurs in both MMC conditions compared with unreinforced alloy. Tensile strengths and elastic moduli are improved in the MMC compared with the alloy, but ductility is reduced. Stretched MMC exhibits higher strength but lower ductility and modulus than re-solutioned MMC. The re-solutioned MMC fails by microvoid coalescence in low aging conditions, and by void nucleation and shear in high aging conditions. Failure of the stretched MMC initiates at the surface at specimen shoulders, illustrating the increased notch sensitivity of this condition, and propagates via a zigzag shear fracture mode. Zigzag facet size increases on gross aging. Particle fracture occurs during tensile failure, but also before testing as a result of the manufacturing process. © 1995 The Institute of Materials.