Comparison of in situ nanocrystals, Sr and nanocrystals + Sr manipulating microstructures and mechanical properties of eutectic Al–Si13.0–Cu5.0–(Ni2.0)–Mg0.6 alloy

Abstract

Trace in situ nanocrystals crystallized from metallic glasses as innovative microstructure manipulation agents were proposed to manipulate the multilevel microstructure configuration of eutectic Al–Si13.0–Cu5.0–Mg0.6 alloy. And the manipulation effect by nanocrystals for different times was compared with Sr, nanocrystals + Sr and Ni alloying. The calculations indicated that NiTi nanocrystals had an ideal mismatch with α-Al and silicon; thus, nanocrystals can stimulate their nucleation and hinder their growth. Sr and Ni alloying were found to only refine the silicon phases, but nanocrystals refined both α-Al and silicon phases. Moreover, the inhibition of nanocrystals and Sr was verified. After the manipulation by nanocrystals for 20 min, the optimum microstructure configuration and mechanical properties were realized. The results showed that the size of α-Al was reduced by 86.7%, and the size and aspect ratio of eutectic silicon were decreased by 27.7% and 50.0% compared with that of the unmanipulated alloy. Primary silicon was distributed more evenly and reduced in number. In addition, the size of Al2Cu and Mg2Si was decreased by 57.7% and 90.6%. Accordingly, a prominent microstructure configuration comprised of refined α-Al, silicon phases and precipitations was established successfully via nanocrystals. Moreover, the ultimate tensile strength (UTS) and fracture strain (FS) were increased by 17.8% and 73.3% compared with that of the unmanipulated alloy at ambient temperature, and the yield strength (σ0.2) and UTS were increased by 21.5% and 14.4% at 250 °C. The specific strengthening mechanisms were revealed, as well. Therefore, in situ nanocrystals have great application potential and developmental value.