Microcasting of Al bronze: influence of casting parameters on the microstructure and the mechanical properties

Abstract

In this work the influence of the casting parameters on the microstructure and the mechanical properties of extremely small parts produced by microcasting was investigated. Different specimens were cast using an aluminum bronze with a composition defined by DIN EN 17 665. It was found that the yield stress and the ultimate tensile strength of micro tensile test specimens increase when decreasing the mold temperature from 1,000 to 700°C. This correlates with the increasing fineness of the microstructure. Additionally, the investigation showed that the mechanical strength of micro-specimens is higher than the one of macrospecimens cast at the same mold temperature due to a finer microstructure which hinders dislocation movement.

New results on microcasting of Al bronze

“…The effect of mold temperature on the specimens' microstructure presented in Fig. 1a-d is not as pronounced as reported in (Baumeister et al 2007a, b;Baumeister et al 2008). Whilst the a-phase is clearly dominant in both cases, its size and morphology as well as the overall specimen microstructure do not compare well with recent results.…”

“…This fact could be explained by the lower cooling rate of the mold with T m = 1,000°C, because reduced quenching effect supports the development of this phase. Investigations on the source of the microstructural differences between specimens in the present study and that in (Baumeister et al 2007a, b;Baumeister et al 2008) reveal that neither the geometry of the runner and sprue system (V-shaped compared to T-shaped for present study) nor the slightly lower amount of material (16 vs. 20 g for this study) have significant influences on the microstructure. The starting materials used in both studies have the same nominal chemical composition which allows a certain range.…”

“…This result offers the possibility of exploiting abrasive peening as a route to improve the fatigue properties in cast micro-parts. It has to be mentioned that the residual stress values obtained in the as-cast and post-treated conditions are well below the ultimate strength of this material 750-1,200 MPa cast at various mold temperatures (Baumeister et al 2007a, b;Baumeister et al 2008).…”

“…In more recent studies (Baumeister et al 2004a, b;Baumeister et al 2008) with better statistics, the flow length in fibers with a diameter of 113 or 238 lm, is seen to rapidly increase in a sudden manner within a low pressure domain before attaining a maximum value and remaining relatively constant over a wide pressure range. In the present study these investigations were extended to a wider range of mold temperatures and filling pressures in order to validate correlations discussed in the above publications (Baumeister et al 2004a, b;Baumeister et al 2007a, b;Baumeister et al 2008). …”

“…These studies have contributed to a better understanding of micro fabrication. It has been shown that the tensile strength of cast aluminum bronze micro tensile test specimens increases with decreasing mold temperature (Baumeister et al 2007a, b;Baumeister et al 2008). However, specimens which were cast at low mold temperatures reveal a markedly higher scatter regarding tensile strength compared to those cast at higher mold temperatures.…”