Spray forming is a novel rapid solidification technology. During spray forming, a liquid metal stream is atomized into a spray of droplets by high-pressure gas jets and subsequently these atomized droplets are deposited and solidified on a substrate. By optimization of the processing parameters, near net shape products, such as strip, tube, and cylinder billet can be produced with a refined microstructure, extended solubility of alloying elements and reduced microsegregation. In this thesis, the researches on the solidification behaviors of the atomized droplets and the spray cone have been carried out by the numerical simulation method. The spray forming parameters of some alloys have been optimized on the base of this model. Several alloys have been successfully prepared by spray forming. The main results are summarized as follows：
1. A numerical model based on the discrete-particles method is developed to describe the solidification process of an atomized droplet during the spray forming. This model is coupled with the heat transfer controlling equations for droplet to simulate the solidification process of the atomized droplets. The solidification of the spray cone was simulated by using the model developed based on the population dynamics method. The results show that the model describes the microstructural development well and is helpful in the optimization of the spray forming parameters.
2. Magnesium alloy AZ91 has been successfully prepared by spray forming. The effect of the thermo-mechanical treatments on the microstructure and mechanical properties of the alloy was studied and the strengthening mechanism was analyzed. The results show that the spray-formed AZ91 alloy has, compared with the as-cast ingot, a finer microstructure with less intermetallic phase of Mg17Al12 dispersed in the matrix and, therefore, shows an excellent workability. It can be hot-rolled with 10~20% reduction for one pass. The spray-formed alloy exhibits outstanding mechanical properties after proper thermo-mechanical treatments.
3. Cu-1.2wt.%Cr and Cu-3.2wt.% Cr alloys were prepared by spray forming. The effects of the chromium content and the thermo-mechanical treatment on the microstructures and mechanical properties of the spray-formed alloys have been investigated. The microstructural features of the Cu-Cr alloys after different thermo-mechanical treatments were characterized by using optical, scanning electron and transmission electron microscopy. The results show that the spray-formed Cu-Cr alloys exhibit a good aging response compared with the conventional casting alloys, indicating that the alloys experience a rapid solidification process. Coherency strengthening is the main strengthening mechanism. Although a higher content of chromium leads to a larger volume fraction of the chromium precipitations generated during the solidification, it does not cause an increase in the mechanical properties. The content of chromium should be lower than 1.2wt.%
4. A bronze with higher tin content (Cu-13.5wt%Sn) was prepared successfully by spray forming. The feasibility of cold rolling this alloy was investigated. The results indicate that the spray-formed Cu-13.5wt%Sn alloy, in contrast to the as-cast ingot, shows a quite fine and homogeneous single-phase structure and, therefore shows an excellent workability. It can be cold-rolled with nearly 15% reduction in the thickness per pass and the total reduction can reach 80%. The classical limit to the Sn content for the wrought and the cast Cu-Sn alloys is shifted considerably to a higher level by spray forming. After proper thermo-mechanical treatments, the spray-formed Cu-13.5wt%Sn alloy exhibits excellent comprehensive mechanical properties. Particularly, it shows a low elastic modulus (~88GPa) and a high flow stress (over 800MPa) after cold forming. This combination of properties is unique in the domain of metallic materials and could open new possibilities in spring technology field.
5. 70wt.%Si-Al alloy was prepared by spray deposition. Hot isostatic press technique （HIP） was adopted to compact the billet. It is found that that the spray formed 70%Si-Al alloy shows a microstructure with fine silicon particles (10~20μm in diameter) dispersed in the matrix. The alloy exhibits excellent comprehensive properties. Especially it has a lower thermal expansion coefficient and a lower density compared with the traditional electronics packaging materials. After HIP, the comprehensive properties of the spray-deposited 70wt.%Si-Al alloy are further enhanced. The alloy can be machined with the traditional cutting tools and applied as the packaging materials for the power interchange, microwave electronic parts and integrate circuit blocks.
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