The hot compression test of Au-20Sn alloys with different solidification structures was carried out. The deformation behaviors and microstructure evolutions during hot compression were investigated. The results indicate that the fine fully lamellar eutectic structure without primary phase exhibited a very low yielding stress and a low stress platform, while the coarse lamellar with large primary Au5Sn phase showed rather high in that value. After compression, the lamellar eutectic tended to be equiaxed due to dynamic recrystallization, the large primary phase became separate dendrites or split into small dendrites, and the small roselike primary phase partly dissolved in the eutectic matrix. The rate of recrystallization also increased as the primary phase eliminated and lamellae was refined. It is suggested that refining eutectic lamellae and eliminating the primary Au5Sn phase in the as-cast microstructure by solidification optimization are an effective way to improve the workability greatly for brittle Au-20Sn eutectic alloy.

The effects of cold rolling, solid solution, aging and annealing treatment on Pt-0.7Ti microalloy were investigated in this study. The microstructures of Pt-0.7Ti microalloy and the precipitated ordered phase Pt8Ti were observed and analyzed by OM, TEM, XRD. The mechanical properties of the alloy were evaluated Vicker micro-hardness. The results showed that micro amount of Ti was an effective element for solid-solution strengthening of Pt, the micro-hardness of 97% deformation for ST and ST+AG samples increased to 214HVand 224HV, respectively, which almost are double that of pure Pt. Micro-amount of long range ordered phase Pt8Ti was precipitated during the heat treatment, but the effect of order hardening in Pt-0.7Ti microalloy was not obvious. The microhardness by large rolling deformation for quenched samples almost unchanged after an annealing below 500°C for 1h, but decreased significantly at 700°C, and the recrystallization temperature was risen by 200°C than that of pure Pt.

The sub-rapidly solidified Au-20Sn eutectic alloys were prepared by four different solidification pathways, such as, graphite mold conventional casting, graphite mold injection casting, copper mold injection casting, and water-cooled copper mold suction casting. The precipitating sequences of competing primary phases of sub-rapidly solidified Au-20Sn alloys with four different cooling rates were investigated. The results show that phase selection process is related to the cooling rates during sub-rapid solidification process. The primary ζ'-Au5Sn phase with developed dendrites precipitate at low cooling rate (2.4×10−4.2×102K/min) and the morphologies of the primary ζ'-Au5Sn change to rosette-like at higher cooling rate (9.0×103K/min). While the cooling rate reaches to 3.5×104K/min, the primary ζ'-Au5Sn phase can be suppressed but δ-AuSn phase will precipitate prior to the ζ'-Au5Sn phase. On the basis of the classical nucleation theory and transient nucleation theory, the process of competitive nucleation between the ζ'-Au5Sn phase and the δ-AuSn phase were analyzed for sub-rapid solidified Au-20Sn alloy. The theoretical calculations are consistent with the experimental investigations.

The PtTi0.5Zr0.2/Ti laminated composite was prepared by hot pressing and rolling process. Microstructure, interlaminar spacing and mechanical property of the microlaminated composites after rolling were evaluated. The results showed that the layer structures of laminated composites remained consecutiveness with 93% deformation. The 12μm PtTi0.5Zr0.2 layer and 8μm Ti layer was observed finally, as well as the intermetallic compound Ti3Pt making the PtTi0.5Zr0.2 layer and Ti layer connect with each other. Compared with Platinum and Titanium, the tensile strength of PtTi0.5Zr0.2/Ti laminated composite was enhanced by approximately 59% and 29% respectively and reached 657MPa. The tensile fracture was more uniform and showed a more coordinated process.

Au-20Sn (mass fraction) eutectic alloy is a key lead-free solder material for high reliability microelectronics and optoelectronics packaging. The refinement of initial solidification structure can improved the processing performance of Au-20Sn alloy. This paper reported the research progresses on refining solidification structure of Au-20Sn alloy in our research group. The results indicated that the solidification structure of alloy can be effectively refined by rapid solidification with the increasing of cooling rate. The solidification structure can also be refined by incubated nucleation treatment with Au or Sn or by proper melt temperature treatment. The refinement mechanisms of solidification structure by the three types of solidification methods were thoroughly discussed.