On Preparation Of Aluminum Foam Sandwich By Packet Rolling-Powder Metallurgy

Characterized by its light weight, high specific strength and stiffness, aluminum foam sandwich has overcome such disadvantages of the bare aluminum foam boards as lower strength, difficulties in surface treatment and connection. It could be broadly applied in areas like automobile manufacturing, aviation, aerospace and rail transportation, etc. Therefore, it is a popular research direction for the development of porous metal foam products and the theoretical study. At present, the preparation of aluminum foam sandwich is mainly through glue-binding and hot press-powder metallurgy foaming process, thus the products have low intensity of board/core combination, poor resistance to high temperature and low productivity. Therefore, it will be of great application value and theoretical significance to develop a new aluminum foam sandwich preparation technology with higher efficiency and shorter process.With the support from The National Natural Science Funds Program (No.50704012) and Shenyang Science and Technology Program (F10-205-1-59), this thesis will focus on the development and theoretical research on the new technology of aluminum foam sandwich preparation. To advance powder utilization and improve plate quality, the process of preparation of aluminum foam sandwich by packet rolling-powder metallurgy was come up. This thesis will study systematically the impact of main process parameters on the foaming effect, and will probe into the relationship between such factors as the rolling reduction rate, foaming temperature, time of foaming and the core foam structure of the aluminum foam sandwich. Through an analysis of the binding mechanism of panel/core powder, the optimized preparation conditions are determined. The surface treatment to the foaming agent TiH2has significantly improved the uniformity and stability of the foaming structure. There is also further analysis on the evolution process of foaming structure and stabilization mechanism. What’s more, after the test of main mechanical properties of the sandwich panel, there is also an investigation of the sandwich structure’s impact on the mechanical properties from both perspectives of foaming structure and the binding state of panel/core. The following are the valuable results of this thesis:1. The adoption of packet rolling has greatly increased the powder utilization ratio, and there is almost no loss of the mixed powder after being rolled and the powder utilization ratio is near to100%. In addition, during the rolling process, the behavior of core powder is consistent along the width of rolled piece. This has not only ensured the high density of the core powder of the preset, but also the significant improvement of the overall uniformity of the powder. Considering both the density of powder and panel/core binding effect, the rolling reduction ratio should better be controlled at60%to70%.2. The homemade steel mold could help to achieve rapid and limited foaming, and the time of foaming has shortened from8～10minutes of free foaming process to less than1-2minutes and it has reduced the possibility of the formation of broken and connecting hole. Limited foaming has ensured good thickness and precision of the foam aluminum sandwich. The ideal foaming process in this research should be700℃of foaming temperature and60s-70s of foaming time.3. The surface modification on the foaming agent TiH2could adjust its decomposition and the process of hydrogen release, thus making the temperature of peak hydrogen release and the amount of hydrogen release meet the foaming process requirements. The optimum heat treatment process in this research should be500℃for60minutes.4. It could improve the mechanical properties of the Al-Si alloy at room temperature and better its processing properties by adding some magnesium in it. The adding of Mg particles could increase viscosity of the melts, thereby reduce the differential pressure between the Plateau border and the foaming wall to increase the stability of the foaming holes. The ideal quantity of the added Mg in this research should be about1.0wt.%to increase viscosity of the melts and greatly increase the stability of the foaming holes of the aluminum foam sandwich. 5. The three-point bending test data of aluminum foam sandwich shows that the maximum load of the aluminum foam sandwich prepared in this research is0.86kN-0.96kN, which is significantly higher than that of the glue-bonded aluminum foam sandwich0.47kN-0.87kN. What is more, the panel and the core could maintain intact after the aluminum foam sandwich being broken, which means there is no panel separation or panel folds. The load-displacement curve shows that the aluminum foam sandwich prepared in this research has a good capacity of energy absorption.6. The aluminum foam sandwich prepared in this research has good impact properties, and the maximum load could reach to0.73kN～1.24kN. The increase of both panel thickness and core thickness of the aluminum foam sandwich will help to improve its impact strength.