Diffusion bonding experiments followed by tensile testing were conducted on cylindrical pairs of AA6061–AA1050 aluminum alloys. The influence of bonding time, atmosphere and surface roughness on the resulting interface strength was studied. Metallurgical characterization was performed to study the quality of the bonded interface for different process conditions, and also to investigate the process of oxide formation on the specimen surface. Finite element analysis of the bonding experiments was used to study the thermo-mechanical fields during the bonding process. Using a cohesive zone approach for modelling the bonded interface, the bond strength for the different process parameters was quantified. The results demonstrate that high bond strength can be obtained even for specimens bonded in an air furnace, provided the surface roughness is low. When the surface roughness increases, specimens bonded in air show a reduction in interface strength, which is not observed for specimens bonded in vacuum. Inspection of the bonded interface suggests that this reduction in interface strength can be attributed to oxidation and pockets of air trapped between the asperities of the contact surface, which hinder diffusion and plastic flow.

The impact of weak particle-matrix interfaces in aluminum matrix composites (AMCs) on effective elastic properties was studied using micromechanical finite-element analysis. Both simplified unit cell representations (i.e., representative area or volume elements) and “real” microstructure-based unit cells were considered. It is demonstrated that a 2D unit cell representation provides accurate effective properties only for strong particle-matrix bond conditions, and underpredicts the effective properties (compared to 3D unit cell computations) for weak interfaces. The computations based on real microstructure of an Al–TiB₂ composite fabricated using spark plasma sintering (SPS) show that, for weak interfaces, the effective elastic properties under tension are different from those obtained under compression. Computations show that differences are the result of the local stress and strain fields, and contact mechanics between particles and the matrix. Preliminary measurements of the effective elastic properties using the ultrasonic pulse-echo technique and compression experiments support the trends observed in computational analysis.

The most accepted method for determining friction conditions in metal forming is the ring compression test (RCT). At high temperatures, extraction of the friction coefficient, μ, commonly requires numerical analysis due to the coupling between the mechanical and thermal fields. In the current study, compression tests of cylindrical specimens and RCT experiments were conducted on commercially pure aluminium (Al1050) at several temperatures, loading rates, and lubrication conditions. The experiments were used in conjunction with a coupled thermo-mechanical finite element analysis to study the dependence of the friction coefficient on those parameters. It is demonstrated that due to the coupling between friction conditions and material flow stress, both μ and flow stress data should be determined from the cylinder and ring specimens simultaneously and not subsequently. The computed friction conditions are validated using a novel method based on identification of the plastic flow neutral radius. It is shown that, due to heat loss mechanisms, the experimental system preparation stage must be incorporated in the computational analysis. The study also addresses the limitation of the RCT in the presence of high friction conditions. The computational models are finally used to examine the thermo-mechanical fields, which develop during the different processes, with an emphasis on the effect of friction conditions, which were then correlated to the resulting microstructure in the RCTs.

The mechanical response and failure of Al-TiB₂ composites fabricated by Spark Plasma Sintering (SPS) were investigated. The effective flow stress at room temperature for different TiB₂ particle volume fractions between 0% and 15% was determined using compression experiments on cylindrical specimens in conjunction with an iterative computational methodology. A different set of experiments on tapered specimens was used to validate the effective flow curves by comparing experimental force–displacement curves and deformation patterns to the ones obtained from the computations. Using a continuum damage mechanics approach, the experiments were also used to construct effective failure curves for each material composition. It was demonstrated that the fracture modes observed in the different experiments could be reproduced in the computations. The results show that increasing the TiB₂ particle volume fraction to 10% results in an increase in material effective yield stress and a decrease in hardening. For a particle volume fraction of 15%, the effective yield stress decreases with no significant influence on the hardening slope. The ductility (workability) of the composite decreases with increasing particle volume fraction.

In recent years, there has been a growing interest in composite components, which may be designed to provide enhanced mechanical and physical effective properties. One of the methods available to produce such components is joining by plastic deformation, which results in metallurgical bonding at the interface. However, the portions of the interface that are bonded and the inhomogeneity in the bonding strength achieved at the interface tend to be overlooked. In the present study, Al6061 beams were bonded, by hot compression (300–500 °C) to different degrees of reduction. The compression was followed by tensile debonding experiments and the revealed interface was microscopically characterized in order to determine the areas that were metallurgically bonded. The SEM characterization revealed that the actual bonded area is much smaller than the interface contact area. Thermo-mechanical finite element models of the compression stage were used to investigate the thermo-mechanical fields, which develop along the interface and influence the resulting bonding strength. The principal strain field patterns across the interface area were shown to be similar to the experimentally observed temperature-dependent bonding patterns. In addition, a quantitative criterion for bonding quality was implemented and shown to correlate with the experimental findings.