Investigation of the Creep resistance of a Spray-compacted Si-particle Reinforced Al-based MMC (Dispal S270)Donnerstag (27.06.2019) 17:00 - 17:20 Uhr
MMCs exhibit a high potential in modern structures due to many positive attributes. One of these attributes is the heightened creep resistance compared to conventional single or multi phase alloys. The following paper focuses on the creep resistance of spray-compacted Aluminum based alloy (DISPAL S270). This alloy, designed for high temperature applications like turbochargers, cylinder bore liners or pistons can be subjected to temperatures up to 450°C. This is considerably higher compared to unreinforced alloys.
DISPAL S270 microscopically consists of Si-particles with round shapes in an Al-rich α solid solution, which is additionally reinforced by complex precipitates, consisting of among others Ti, Cu, Fe, Cr and Zr. The particle size and the ratio differs with the heat treatment. The same applies to the precipitates. The investigated heat treatments are F, T4 and T6.
The alloy is tested at 250°C and 400°C with different loads at constant force (start stress value 25 MPa - 200 MPa). The measured minimal creep rates are in the range of εmin = 10-8 – 10-51/s. The threshold stress for T = 250°C experiments indicates values of approximately 50 MPa and for T = 400°C approximately 10 MPa. In comparison to conventional single or multiple phase alloys DISPAL S270 reveals some advantages because the threshold stress strongly lowers the resulting stress level and thus reduces the minimum creep rates. The stress exponent can be modified, known from previous MMC studies.
The specimen are analyzed with SEM, EDX and XRD before and after creep. The breakage of the creep specimen arises due to voids, which occur at apexes of the Si-particles and at grain boundaries. During the test, these voids grow bigger and sometimes merge. This voids grow orthogonal to the stress axis. The specimen finally fails due to a declining load bearing cross-section.