This investigation evaluates the abrasive-corrosive wear behaviour of aluminium alloys with the aim of establishing a data base of performance and guide lines for material optimisation. Wear test apparatus and standard tests developed by previous research programmes were utilised (Noel and Allen, 1981; Barker, 1988). Further tests were then devised for a more detailed characterisation of wear behaviour. Tests conducted showed that aluminium alloys have approximately a quarter to half the abrasion resistance of mild steel. Poor microfracture properties of Al-Si cast alloys were observed as a result of coarse and brittle silicon rich phases contained in the aluminium matrix. Non heat-treatable wrought alloys exhibit ductile micro-deformation characteristics whilst heat-treatable alloys, having the best abrasion resistance, possess better combinations of strength, hardness and toughness. Tests with combined corrosion and wear showed that most aluminium alloys are subject to pitting corrosion due to localised differences in electrode potentials at constituent sites. Higher series alloys with a large number of constituent particles exhibit higher pitting densities. Due to the high electrode potentials of silicon phases and copper and zinc solid solutions, the alloys LM6+Sr, 2014 and 7075 have poor corrosion resistance and are subject to localised and pitting attack. As a consequence the alloys 2014, 7075 and LM6+Sr show a decrease in wear performance under abrasive-corrosive conditions. In contrast the good corrosion resistance of the alloys 5083, 6261 and 7017 provide a significant improvement in wear performance under conditions of long corrosion periods with light abrasive intervals. This study concludes that the abrasion resistance of wrought alloys may be optimised by designing an alloy with a good combination of tensile strength, fracture toughness and hardness together with an intermediate microstructural size distribution of second phase particles in the aluminium matrix. Ageing of heat treatable alloys improves abrasion resistance significantly, peak hardness and strength conditions resulting in optimum abrasion properties.

In this dissertation, the fatigue characteristics of three newly developed experimental compositions for aluminum 7175, with improved mechanical strength, that uses magnesium-calcium alloy instead of pure magnesium are studied. Specimens of each variant were fabricated and subjected to fatigue life testing, fatigue life data analysis, and observation of their fracture characteristics through optical microscopy and scanning electron microscopy (SEM), and metallography to study their grains and surface characteristics. Fatigue life testing shows all three variants have a fatigue strength that is approaching approximately 200 MPa. ECO7175v3 is shown to have the highest fatigue strength of approximately 220 MPa at 5x107 cycles, approximately 40% of its tensile strength of 550 MPa. This is shown by its considerably higher fatigue strength coefficient determined by Basquin's equation compared to the other two variants. ECO7175v1 is shown to generally have large scatter in its fatigue life at higher stress levels (65% or higher of their tensile strength) with coefficient of variations typically twice or more to those of ECO7175v2 and ECO7175v3. The results of the SEM analysis shows that irrespective of the stress levels, ECO7175v1 and ECO7175v3 all have crack initiation points at the surface with no inclusions to act as stress concentrators. The lack of inclusions are supported by the reliability analysis which shows the hazard rates for all variants remains relatively constant the majority of the time before increasing towards the end. These trends for all variants indicates failures are due to wear-outs instead of defects, which were not seen. Reliability analysis also shows that at any given fatigue life cycle and stress level, ECO7175v3 has a lower probability of failure when compared to ECO7175v1 and ECO7175v2. On the other hand, at any given fatigue life cycle and stress level, ECO7175v1 is shown to have a higher probability of failure when compared to ECO7175v2 and ECO7175v3.

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