Application of T6 Heat Treatment on the AlSi9Cu3 (Fe) Casting Alloy and the Effect of Copper Content

AlSi9Cu3 (Fe) foundry alloy is commonly used to produce components by High Pressure Die Casting (HPDC) for automotive and electrical industries. Mostly for cost reasons, the Cu content is held at the minimum of the compositional range foreseen by the standards. The strength of the metal is then quite low and therefore the components are used only in low or non-stressed applications. The experimental results of the present paper show that in the as cast temper, the percentage of Cu has little effect on strength. It is suggested that alternative alloys for HPDC with lower or no Cu content be adopted for non-stressed components. In the last 15 years, it has been demonstrated that Al-Si-Cu alloys for HPDC may successfully heat-treated by unconventional T6 without causing surface blistering or dimensional instability. Despite the new opportunities, there have been few industrial applications. Instead, the present authors believe possible new technological outcomes for unconventional T6, and have therefore experimented with the AlSi9Cu3 (Fe) alloy with different Cu contents. By using SEM-EDX microanalysis to get Cu composition maps in the alloy microstructure, a T6 heat treatment with lower solubilization temperature and shorter soaking time to avoiding blistering has been identified. Tensile test confirmed the effectiveness of unconventional T6 and showed a strong increase in the elastic limit of the material. The results also show that the best effect is obtained by increasing the Cu content as much as possible. It is therefore possible to produce components for highly stressed structural applications in T6 treated AlSi9Cu3 (Fe) alloy

Influence of Process Parameters and Deposition Strategy on Laser Metal Deposition of 316L Powder

In blown powder additive manufacturing technologies the geometrical stability of the built parts is more complex with respect to more conventional powder bed processes. Because of this reason, in order to select the most suitable building parameters, it is important to investigate the shape and the properties of the single metal bead formation and the effect that a scan track has on the nearby ones. In the present study, a methodology to identify an appropriate laser metal deposition process window was introduced, and the effect of the building parameters on the geometry of circular steel samples was investigated. The effect of the scanning strategy on the deposited part was also investigated. This work draws the attention to the importance of the obtainment of the most suitable melt pool shape, demonstrating that the laser power and the scanning strategy have a strong influence not only on the shape but also on the mechanical properties of the final component

Influence of microstructural heterogeneity on the scaling between flow stress and relative density in microcellular Al-4.5%Cu

We explore the influence of the metal microstructure on the compressive flow stress of replicated microcellular 400-μm pore size Al-4.5wt%Cu solidified at two different solidification cooling rates, in the as-cast and T6 conditions. It is found that the yield strength roughly doubles with age-hardening, but does not depend on the solidification cooling rate. Internal damage accumulation, measured by monitoring the rate of stiffness loss with strain, is similar across the four microstructures explored and equals that measured in similar microcellular pure aluminium. In situ flow curves of the metal within the open-pore microcellular material are back-calculated using the Variational Estimate of Ponte-Castañeda and Suquet. Consistent results are obtained with heat-treated microcellular Al-4.5wt%Cu and are also obtained with separate data for pure Al; however, for the as-cast microcellular Al-4.5wt%Cu, the back-calculated in situ metal flow stress decreases, for both solidification rates, with decreasing relative density of the foam. We attribute this effect to an interplay between the microstructural and mesostructural features of the microcellular material: variations in the latter with the former held constant can alter the scaling between flow stress and relative density within microcellular alloys