Obtaining Microcrystalline Al-Ni Alloys with Refined Structures by Rapid 
Quencing from the Melt 
Nicolae Petrescu, Lidia Cristea, Maria Petrescu, Enona Cristea — University “Politehnica” of 
Bucharest — Romania. 
Melt spinning and melt extraction methods of rapid solidification have been applied on a 
wide composition range of Al-Ni alloys. Two important effects of the rapid solidification process 
(also termed “liquid quenching”) have been put in evidence in the microstructure of the examined 
Al-Ni alloys. (i) In the low range of Ni content (0.5 up to 4wt % Ni) a complete extension of the 
solid state solubility has been obtained, resulting in a highly supersaturated o. Al primary solid 
solution. (ii) In the high range of Ni content (10 up to 31wt % Ni) the main structural effect that has 
been put in evidence was an advanced size refinement of the secondary phase particles [1]. 
Concerning the first structural effect of the rapid solidification process, namely the solid 
state solidification extension, its value can be estimated by taking into account the equilibrium 
solubility of Ni in Al equal to 0.006wt % Ni at 500°C. As the nickel content in the supersaturated 
Al solid solution obtained by applying the melt spinning method of liquid quenching at a cooling 
rate up to 10°°C/s was 4wt % Ni in our experiments, a degree of supersaturation of ~667 times has 
been obtained. Such an effect is of uttermost scientific and practical interest because it offers the 
possibility to broaden the number of Al alloys by including the transition metals as alloying 
elements. In normal solidification conditions such elements (manganese is an exception) have to be 
ruled out as alloying elements in Al because of their extremely low solid state solubility as 
exemplified by Ni. For the transition metals, including Ni, the solid state solubility extension 
promoted by rapid solidification is the only way to transform them in useful alloying elements, 
resulting in new high strength Al based alloys, for which very efficient hardening mechanisms are 
put at work, namely solution hardening and precipitation hardening. 
Fig.1: Slowly solidified Al-2wt% Ni alloy. Fig.2: Rapidly solidified Al-2wt% Ni alloy. 
SEM electron micrograph (composition SEM electron micrograph (composition 
image x150) image x150) 
Figures 1, 3 and 5 show the microstructure of the Al-Ni alloys having a nickel content of 2, 
3 and 4 wt % Ni, after applying a slow cooling rate upon solidification. The SEM micrographs, 
recorded as composition images show a progressive decrease of the amount of a Al solid solution 
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