Research On Preparation Technique Of Foamed Aluminum By Powder Metallurgy With Composite Heating

As a new type of functional and structural material, foamed aluminum was widely used in aerospace, automobile and architecture industry recently because of its lightweight, fire retardancy, amortization, high energy absorbing and other excellent physical property. For preforming, less processing later, and its easiness to produce Sandwich material, foamed aluminum produced by powder metallurgy has attracted more and more interests of technologist. As one of the best foaming agent for foamed aluminum, the character of TiH2 will affect foaming process greatly. So studies on the releasing character, surface modification of TiH2, and transformation of foams in faming process and evaluating the foaming effect are benefit to improving the producing techniques, controlling the size of the bubbles and obtaining high porous foams.In this paper the releasing character and surface modification of TiH2 as received and heated in air and oxide changing process in heating have been studied using collecting gas directly and X-ray diffraction (XRD) techniques. Furthermore, a new way of heating precursors has been put forward on the principle of powder metallurgy producing precursors, in which the precursors were heated up immerging into melting Al directly and preserved temperature in Argon. And the effects of the content and surface modification of TiH2, foaming temperature and time, content of Al2O3 on the foam aluminum structure and properties have been investigated specially. Meanwhile, the evolution of foams during the foaming process has been studied. In order to evaluate the foamed aluminum structure, the uniformity coefficient (K) and its expression have been given according to the relative variance.The results show that T1H2 starts to release hydrogen between 380 and 390℃, and during the gas releasing process, three obvious stages appear, and the fastest one is in the second stage which form the β -phase in the eutectoid reaction. Heat treatment can increase the start decomposable temperature, which shows that the oxides can decrease the gas releasing process obviously. Color of TiR2 after the above treatment changes obviously from gray to golden green, yellow, purple, blue with temperature and time changing when heating temperature is lower than 550℃ in the atmosphere. The changes of the color not only show that the oxide thickness change and phase transformation, but also present that oxygenation is a gradual process.The bubble's structure will change from cracks to roundness or ellipse and then to polyhedron in the foaming process. Because of thinning of cell wall and drainage of the melting body, the bubbles will joint together and collapse at the end period of foaming.Content of TiH2 will affect the foamed aluminum porosity and distribution of pores directly. The uniformity of pores will be better with the content increasing of TiH2, but when the content is more than 1.5%, the foaming character will turn worse. Usage of TiH2 and foaming character will be improved after treated in air in a certain optimal treated temperature and time. The heating temperature and time of precursors are the key parameters of producing foamed aluminum when the content of the foaming agent is constant. If heating temperature is higher, the preserving time will be shorter. When the heating temperature are much higher and the preserving time longer, the distribution andporosity of foamed aluminum will decrease. Better foaming character can be gained when temperature and time are 720℃, 120s. Adding 1-3% Al2O3 particles in the precursors can increase melt viscosity, refine bubbles and increase porosity of foamed aluminumFoamed aluminum with the porosity of 88.4% and uniform structure properties could be fabricated by adopting the above methods with optimal parameters. Compare to traditional method, the foaming time reduces from 10min to 30-150s. The test results show that this way possesses well prospect of development and application.