The effect of an electric or magnetic field on transformation of liquid–solid state in materials is reviewed along with the microstructure of the resultant solid. In metals, the electro-migration in the liquid generates significant variations in composition because of the alterations in ionic mobility. Additionally, small, continuous D.C current of approx. 0.1 A cm−2 as well as the high density electropulsing of almost 103 A cm−2 refined the castings of microstructure. Almost >1T magnetic field is applied in directional solidification that significantly lower the convective flow in the metal along with the distortion in cellular array. Whereas, the dendritic array and macrosegregation is not affected by this process. The mechanisms causing the occurrence and their effects on microstructure are yet to be determined. In electropulsing, the effect of the current look as if it enhances the nucleation rate, with deformation at the higher current densities and causes fracture dendrites by pinch effect. The magnetic field influences mainly due to the Lorentz forces that established among motion of the conductive melt and the applied field. Concerning semiconductors, an electric current of 1–10 A cm−2 have the ability to enhance growth rate of GaAs single crystals on a substrate but reduction in the dislocation density of the product is observed. Theoretically, the effects and the experimental results of the treatments are in accordance. In the case of polymers, camphor solution in CCl4 pulled’ a camphor single crystal due to the application of an electric field of ∼1 V cm−1 ‘.
https://www.sciencedirect.com/science/article/pii/S0921509300007772
The solidification behaviour has been investigated in dilute Sc comprising of Al alloys. In binary alloys such as Al–Sc alloys the addition of Sc more than the eutectic composition (0.55 wt%) were reported to produce a notable refinement in aluminium castings grain size, almost two orders of magnitude. The said refinement is the result of formation of the primary Al3Sc intermetallic phase during the process of solidification. The refinement in the size of grain is linked with the hypereutectic compositions and was revealed to be far better than can be accomplished via conventional refiner’s methods for the Al grain. Grain refinement by the adding the Sc is achieved by alterations in growth morphology from dendritic, in case of the large unrefined grain to a very fine spherical grain with a separated eutectic look of the grain boundaries in the polished castings. Comparable levels of refinement were also observed in other alloys which include Al–Sc–Zr as well as Al–Cu–Sc alloys. In the later, modification in the segregation behaviour of Cu from a strong interdendritic segregation pattern was identified in the direction of a further homogeneous distribution. The supersaturated Al–Sc solid solution can decompose by a process of discontinuous precipitation reaction thereby forming a clear rod-like precipitates of the L12 Al3Sc phase.
https://www.sciencedirect.com/science/article/pii/S1359645498002572
In spite of the grain refinement commercial importance and the availability of huge scientific data on this topic its mechanism is still not clear. There are numerous theories on the working principles of commercial grain refiners (Al-Ti and Al-Ti-B), but meticulous analysis revealed that no clear agreement has yet developed. In the current study, the commercial grain refining practice of aluminium has been simulated on experimental basis by the introduction of synthetic TiB2 crystallites into melts by technique particularly developed for the purpose. Experimental results show that TiB2crystallites is unable to nucleate α-Al alone. Instead, presence of dissolved Ti even lower than the peritectic level with the formation of an interfacial TiAl3 layer at TiB2-melt junction thus subsequently nucleates the α-Al. The hypothetical along with the practical consequences of grain refinement mechanisms are discussed keeping in view of the recent experimental findings. The proposed mechanism for nucleation is ‘duplex’ nucleation which is based on the segregation of solute to the substrate/melt interface.
https://www.sciencedirect.com/science/article/pii/0956715194004057
Precipitation strengthening investigation is shown in binary Al–0.1Sc, Al–0.1Zr in addition to ternary Al–0.1Sc–0.1Zr (at.%) alloys old isochronally from 200-600 °C. Precipitation of Al3Sc (L12) begins between temperature range of 200 to 250 °C in case of Al–0.1Sc, along with the accomplishment a 670 MPa peak microhardness at temperature of 325 °C. For Al–0.1Zr, precipitation of Al3Zr (L12) begins at 350 to 375 °C that result in a 420 MPa peak and microhardness at 425–450 °C. A marked synergistic effect is detected in presence of Sc as well as Zr. Above 325 °C temprature, the addition of Zr provides secondary strength increase from the precipitation of Zr-enriched outer shells to the precipitates of Al3Sc thus lead to a peak microhardness of 780 MPa at 400 °C for Al–0.1Sc–0.1Zr. Configurations, radii, volume fractions and quantity densities of the Al3(Sc1−xZrx) precipitates are measured directly by the use of atom-probe tomography. The resultant data obtained is used further for the quantification of the observed strengthening increases, credited to displacement shearing of the precipitates of Al3(Sc1−xZrx).
https://www.sciencedirect.com/science/article/pii/S1359645410003393
Al–Sc and Al–Sc–Zr alloys comprising of 0.05, 0.1 and 0.5% of respective metal by weight. Sc and Zr metals were examined by means of optical microscopy, electron microscopy in addition to X-ray diffraction. The alloy phase composition and the morphology of precipitates that are formed through solidification in the sand casting procedures subsequent to the thermal treatment of the samples were considered. XRD analysis illustrates reported the weight percentage of the Al3Sc/Al3(Sc, Zr) precipitates to be significantly lower than 1% in all alloys apart from for the virgin Al0.5Sc0.15Zr alloy. In case of virgin Al0.5Sc0.15Zr alloy the precipitates were measured as primary dendritic particles. In the binary Al–Sc alloys, ageing for 24 hrs at 470 °C results in the production of precipitates that are related to the dislocation networks, however the precipitates in the annealed Al–Sc–Zr alloys remained free of interfacial dislocations when content of Sc is lowest. Advances towards the development of large disjointed precipitates through the process of precipitation via heat treatment reduced rigidity of all the alloys under study. Progress of the Al3Sc/Al3(Sc, Zr) precipitates subsequent to heat treatment was reduced at lower amount of Sc content and in the existence of Zr. Upsurge in hardness was noticed after 300 °C heat treatment application in all alloys. The small difference in hardness was observed between binary and ternary alloys during the processes such as slow cooled after the procedure of sand casting.
https://www.sciencedirect.com/science/article/pii/S1044580309002204#fig4
Aluminium-rich alloys as in AI-Sc system were scrutinised in order to govern the arrangement of the equilibrium phase diagram along with obtaining information pertinent to the age associated hardening of chill cast alloys. Models covering up to 8.75wt% Sc were studied by means of thermal analysis besides optical microscopy. The work specified a eutectic type of phase diagram with a eutectic temperature and composition of about 665~ and 0.6wt% Sc respectively. The scandium-rich primary phase was reported to be ScAI3 which is of fcc with a framework parameter of 0.4105 nm. Chill cast samples with 1 wt% Sc alloy were observed for their age hardening behaviour over the range of temperature typically from 225 to 360~ C. A maximum hardness of 77 VHN was attained subsequently after 3 days of ageing at 250~. The achieved hardness was retained for at least 12 days of ageing. The hardening precipitates were observed to produce by a discontinuous precipitation phenomenon. The ScAI3 precipitates were also found to be in parallel positioning relationship with the matrix.
https://link.springer.com/content/pdf/10.1007%2FBF00553049.pdf
The Al3Sc precipitation of primary particles within aluminium alloy melts is of significant technological implication as a fact that robust grain refining outcome on cast structures. The nucleation attribute along with the growth morphology of the Al3Sc primary particles formed in a slightly hypereutectic Al–0.7Sc alloy have been under investigation. For this purpose, a range of cooling rates in a FEG-SEM, by the use of extracted particles, in addition to the TEM analysis is employed. Results indicated that within the melts the Al3Sc particles nucleate heterogeneously on oxides. At slow cooling rates of almost ∼1 K s−1 the particles displayed faceted growth thus establishing {100} faceted particles having cubic shaped and larger particles contained numerous attached cubes. At higher cooling rates of approx. 100–1000 K s−1 the particles’ interface turns out to be unstable typically from the cube edges and corners thus formation of growth perturbations was observed thereby leading to the formation of particles that are still stick to to an complete cubic morphology, but then cellular–dendritic sub-structures do exist.
https://www.sciencedirect.com/science/article/pii/S1359645401000507#FIG2
The roughening behaviour of the Al3Sc particles in Al with 0.2wt%Sc alloy at 673 to 763 K is examined based on the TEM observations along with numerical model. Emphasis is made on the effects of coherent and/or semi-coherent conversion of the particles. The determination of the Al3Sc particles radius for coherent/semi-coherent transition is obtained by the TEM micrographs that is reported to be 15–40 nm. The average Al3Sc particles radius, rave, obeys the rave3 growth low in the coherent stage (rave<15 nm) as well as the semi-coherent phase (rave>40 nm). Still, in the intermediate stage, where coexistence of the coherent and semi-coherent particles is reported to be (15<rave<40 nm), coarsening is late with the widening of the particle size distribution in the experimental model. The above results showed qualitative consideration of the individual particle difference in the growth rates during the the intermediate stage.
https://www.sciencedirect.com/science/article/pii/S1359645403006104#FIG2
The effects of various heat treatments on the microstructure as well as mechanical properties of a rolled 5754 aluminum alloy altered with 0.23 wt.% Sc and 0.22 wt.% Zr were considered. Grain size, precipitate size, type along with the morphology were under observation by techniques of optical and transmission electron microscopies. Two types of the Al3Sc1−xZrx phase were present. Firstly, large incoherent precipitates formation during the solidification and hot-rolling; and the other category which is finely coherent precipitates due to the secondary precipitation thus improving the alloy strength supported by the hardness, tensile, and fatigue calculations. Maturing, though produced two types of grain-boundary precipitates i.e. Al6Mn and β-Al3Mg2, thus contributed to inferior fatigue behavior with reduced ductility.
https://www.sciencedirect.com/science/article/pii/S0921509302000564#FIG10
A current experimental examination of selected compositions in the Al–Sc phase deviates expressively from the previous reported data. Mostly the determined invariant temperatures are dissimilar. It is also found that the AlSc2 phase melts correspondingly, as proposed by the previous work at approx. 1300 uC temperature. The most visible difference is the extensive solid solubility of Al in b-Sc as well as the transformation of eutectoid b-Sc~AlSc2za-Sc that occur at approx. 970uC. Still, it has been recommended that the AlSc phase to some extent is off-stoichiometric with the composition ranged between approximately 52% to 54%Sc.
https://www.tandfonline.com/doi/pdf/10.1179/174328005X14311?needAccess=true
The composition effects, cooling rate subsequently to the solidification and annealing regime on the assembly and hardening of binary as well as the ternary alloys of Al–Sc–Zr system are under review. The liquidus in Al–Sc–Zr alloys is experimentally evaluated thus facilitating to choose correctly the casting temperatures. During slow cooling, the precipitation after the end of solidification is associated with the hardening in the as-cast state with reductions in the hardening effect is observed during annealing. It is shown that the complete hardening capability of precipitates can be attained only upon their homogeneous distribution within the matrix. The optimal entire concentration of Sc and Zr in aluminium alloys should be around 0.3 wt% having ratio of Zr: Sc = ‡ 2 thereby allowing the conventional casting temperatures in addition to the achievement of the considerable hardening during the process of annealing.
https://link.springer.com/content/pdf/10.1007%2Fs10853-006-0265-7.pdf
A sequence of Al–Mg alloy plates having 4mm thickness having slight Sc and Zr were synthesized along with investigating the microstructure and tensile properties of these alloys. The results showed that addition of almost 0.2% Sc and 0.1% Zr to Al–5Mg alloy increases the strength by 150 MPa. In Al alloys, strengthening effect is the considered to be the most extraordinary among all minor alloying elements. Strength increment produced by addition of minor Sc and Zr is credited mostly to fine grain strengthening, precipitation strengthening of Al3(Sc, Zr) and also the substructure strengthening.
https://www.sciencedirect.com/science/article/pii/S0921509399006826#FIG3