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Interfacial solute clustering is an essential step preceding grain boundary (GB) precipitation. Both states, i.e., clusters and precipitates, alter the mechanical, chemical, and corrosion properties of materials. Continuum models cannot capture the atomic details of these phenomena, specifically of the transition from clustering to precipitation. We thus use the structural phase-field crystal (XPFC) model to study the compositional and structural evolution during GB clustering in Al-Cu alloys. The results show that the compositional evolution is dominated by solute segregation to lattice defects at the very beginning and then by confined spinodal decomposition along the GBs. The latter leads to a steep increase in the concentration and then the formation of disordered clusters. This structure acts as a precursor for phase nucleation, just like the decomposed solid solution, and Guinier-Preston zones are the precursors of the thermodynamically stable Al 2 Cu phase in the interior of grains. Two modes of spinodal decomposition are found. (a) On low-angle tilt GBs, spinodal decomposition occurs at the dislocations that constitute the GB. (b) On high-angle tilt GBs, spinodal decomposition takes place inside the entire GB plane. In either case, the structural transition from the disordered low-dimensional precursor states to an ordered phase state takes place following the compositional enrichment. These results shed light on atomic-scale early-stage GB decomposition and precipitation processes in Al-Cu alloys and enrich our knowledge about the coupling effects between compositional and structural evolution during GB phase transformation phenomena.

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Based on the solidification features of ductile iron and affecting factors for ductile iron shrinkage defect, the model of the ductile iron solidification is built and put forward a new defect predictive method EIECAM (Enclosed-Isolated area Expansion and Contraction Accumulation Method) model to predict defect. in DECAM, the liquid shrinkage, solidified shrinkage and graphitizing expansion during solidification are computed dynamically in the enclosed-isolated area , and the effect of graphite expansion on the wall movement is also accounted. Based on this method end cover of QT500 ductile iron casting is simulated and made the defect predictive, study its solidification process and the defect generation position, and make the experimental identification on the defect. It is resulted that the method can be able to predict the casting defect authentically.

The 7A62 as one kind of Al-Zn-Mg alloys is the highest strength weldable aluminum alloy currently. Plates and forgings of 7A62 alloy have been widely used in the defense system and main bearing parts of special vehicles. The microstructure, dynamic mechanical response and weldability of 7A62 aluminum alloy were investigated by OM, TEM, SHTB, DSC, microhardness and other tests. The morphology and mechanical test results showed that the 7A62 aluminum alloy strengthened by trans-scale precipitates had high strength, high hardness and good plastic toughness. The mechanical responses of the 7A62 aluminum alloy were found to be strain-rate sensitive and the dynamic response behavior was significantly higher than that of the 7A52 aluminum alloy through the SHTB test. In addition, for the as-welded 7A62 the tensile strength reached a scope of 260 MPa-305 MPa, which is considerably higher than the tensile properties reported when using ER5356. Because the weld of 7A62 alloy was free of macroscopic imperfections. The grains were highly equiaxed and homogeneous throughout the melting zone, showing smooth grain boundaries. Compared with 7A52, the lower melting point, low thermal enthalpy and low specific heat capacity of 7A62 alloy are more conducive to weld performed.