Supportive strengthening role of Cr-rich phase on Al–Si multicomponent piston alloy at elevated temperature

The microstructure and elevated-temperature strength of an Al–Si piston alloy with 0.5 wt.% Cr and 0.8 wt.% Fe addition were investigated in this paper. The addition of Cr and Fe leads to the formation of α-Al(Fe,Cr)Si phase, which maintains the crystal structure of α-Al(Fe,Mn,Cr)Si phase but has different stoichiometry and morphology from the phase in previous works. Besides, the morphology of δ-Al3CuNi phase changes because of solid-solved Cr. These changes result in the formation of closed and semi-closed network eutectic colonies. The Cr-rich phases, acting as effective supportive strengthening phase, integrate organically with Ni-rich phases, acting as main strengthening phases. So α-Al phases are successfully encircled by eutectic intermetallic phases, and the slide of α-Al under stress at elevated temperature can be effectively hindered. Thus the ultimate tensile strength of the examined alloy is increased by 26% after 0.5 wt.% Cr and 0.8 wt.% Fe addition.

Research highlights
► The UTS of the alloy is increased by 26% at 350 °C.
► Supportive strengthening phase α-Al(Fe,Cr)Si forms and integrates organically with Ni-rich phases.
► The morphology of δ-Al3CuNi phase changes because of solid-solved Cr.
► Closed and semi-closed network eutectic colonies form and α-Al phases are successfully encircled.