Search

The varied mechanisms of yttrium (Y) modifying a hypoeutectic Al–Si alloy under conditions of different cooling rates were investigated using solidification curves, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), transmission electron microscopy (TEM) equipped with energy dispersion X-ray detector (EDX) and high resolution transmission electron microscope (HRTEM). The results show that Y could modify the eutectic silicon of a hypoeutectic Al–Si alloy (A357), but the modification mechanism was different at variable cooling rates. At a low cooling rate, Y modified the eutectic silicon by introducing additional nucleation cores during the nucleation process. At a high cooling rate, Y modified the eutectic silicon by promoting the twin formation during its growth process. • The varied modification mechanism of yttrium (Y) on hypoeutectic Al–Si alloy at different cooling rates was investigated. • At low cooling rate, Y modified eutectic silicon through introducing more nucleation cores during its nucleation process. • At high cooling rate, Y modified eutectic silicon through promoting the formation of twins during its growth process. [ABSTRACT FROM AUTHOR]

• The effects of Cu or Zn on the fluidity of A357 alloy were investigated. • With increase of Cu or Zn content, the fluidity of A357 alloy decreased. • With increase of Cu or Zn, the solidification temperature range increased. • The coarse grain is not the main reason for the fluidity to deteriorate. Excellent fluidity is an essential condition for Al-Si-Mg alloy (like A357) to make large thin-walled and complex structure castings, but t here is no research about the effects of Cu or Zn on the fluidity of Al-Si-Mg alloys. Under sand casting conditions, the effects of Cu or Zn on the fluidity of A357 were investigated through spiral fluidity resin sand molds, DSC, polarizing microscope and SEM. The results showed that with increase of Cu or Zn content, the solidification temperature range (T) of A357 alloy increased, and the fluidity decreased. With Cu or Zn addition, the grain size of A357 alloy increased, but the coarse grain is not the main reason for the fluidity to deteriorate. [ABSTRACT FROM AUTHOR]

• As for grains of Al-Si-Mg alloy, the poisoning effect of Zr and Ti-B occurred. • As for grains of Al-Si-Mg alloy, the poisoning effect of Sc and Ti-B was studied. • The order of grain size was A357 (Al-Si-Mg alloy) < A357 + Zr < A357 + Sc. • The content of Ti as nucleation cores in the melt decreased. • The poisoning occurred in the nucleation stage of grains. The effects of Sc or Zr on the grains of Al-Si-Mg alloy with Al-Ti-B addition were investigated under sand casting conditions by a polarizing microscope, differential scanning calorimetry and scanning electron microscopy. The results showed that the order of grain size is Alloy 1 (A357) < Alloy 3 (A357 + Zr) < Alloy 2 (A357 + Sc), which meant that when Zr and Ti-B existed at the same time or Sc and Ti-B existed at the same time, the grain refinement effect of Zr, Sc and Ti-B can not be reflected, and the poisoning occurred. The order of the actual nucleation temperature of primary α-Al grains (T l) was Alloy 1 > Alloy 3 > Alloy 2. In Al-Si-Mg alloy with Ti-B, with added Sc or Zr, many intermetallic compounds containing Sc and Ti or Zr and Ti appeared, which meant that the content of Ti as nucleation cores in the melt decreased, and the poisoning occurred in the nucleation stage of grains. [ABSTRACT FROM AUTHOR]

• The effects of yttrium (Y) on the primary α-Al and precipitation of A357 alloy were investigated. • With Y addition, the primary α-Al nucleation was more difficult. • The primary dendrite arms became longer and narrower, and the secondary dendrites had longer arms and smaller arm spacing. • With Y addition, the number of β″ decreased. Under sand casting conditions, the effects of yttrium (Y) on the primary α-Al and precipitation of A357 alloy were investigated. The results showed that with Y addition, the primary α-Al nucleation was more difficult, and the Tliquidus-Tsolidus decreased. Meanwhile, the number of the dendritic primary α-Al grains increased, the primary dendrite arms became longer and narrower, and the secondary dendrites had longer arms and smaller arm spacing. Some other elements had the same phenomenon, like Si, Sr, etc. As for precipitation, with Y addition, the number of β″ decreased. Y did not affect the β″ habit plane and did not change the types or produce new precipitation. [ABSTRACT FROM AUTHOR]