Pore structure and mechanical properties of directionally solidi ed porous aluminum alloys

Porous aluminum alloys produced by the metal-gas eutectic method or GASAR process need to be performed under a certain pressure of hydrogen, and to carry over melt to a tailor-made apparatus that ensures directional solidif ication. Hydrogen is driven out of the melt, and then the quasi-cylindrical pores normal to the solidif ication front are usually formed. In the research, the effects of processing parameters(saturation pressure, solidif ication pressure, temperature, and holding time) on the pore structure and porosity of porous aluminum alloys were analyzed. The mechanical properties of Al-Mg alloys were studied by the compressive tests, and the advantages of the porous structure were indicated. By using the GASAR method, pure aluminum, Al-3wt.%Mg, Al-6wt.%Mg and Al-35wt.%Mg alloys with oriented pores have been successfully produced under processing conditions of varying gas pressure, and the relationship between the f inal pore structure and the solidif ication pressure, as well as the inf luences of Mg quantity on the pore size, porosity and mechanical properties of AlMg alloy were investigated. The results show that a higher pressure of solidif ication tends to yield smaller pores in aluminum and its alloys. In the case of Al-Mg alloys, it was proved that with the increasing of Mg amount, the mechanical properties of the alloys sharply deteriorate. However, since Al-3%Mg and Al-6wt.%Mg alloys are ductile metals, their porous samples have greater compressive strength than that of the dense samples due to the existence of pores. It gives the opportunity to use them in industry at the same conditions as dense alloys with savings in weight and material consumption.

SIMULATION OF LIQUID ALUMINIUM INFILTRATION IN POROUS MEDIUM

Based on the principle of infiltration mechanics in porous medium, high Reynolds number infiltration of liquid aluminum in porous medium has been investigated. Combined with the test results of hydraulic simulation, the mathematical model of the high Reynolds number infiltration of liquid aluminum in porous medium has been established, and it is found that infiltration is characterized by its second order nonlinear. The calculated results based on the model are in good agreement with those of the hydraulic simulation and the aluminum alloy infiltration. The way of high speed infiltration under medium pressure has been put forward to fabricate porous aluminum alloy with thin holes of 0.4mm diameter.

A kind of double-sided porous anodic alumina membrane fabricated with the three-step anodic oxidation method

The porous anodic alumina membranes （PAAMs） have been successfully used as templates for the fabrication of functional nano-materials due to their outstanding regularity and physicochemical properties. In this paper, a transparent double-sided anodic alumina membrane with ultra-thin aluminum substrate was fabricated with the three-step anodic oxidation method in the oxalic acid electrolyte. The characters such as the top-surface morphology, membrane thickness, and depth of nanopores of this three-layer （A1203-A1-A1203） sandwiched nano-structure were controllable through regulating the main anodic oxidation conditions, e.g., anodic oxidation time of various steps, coating remove process. The experiments data revealed that the aluminum substrate is exponential declined with the oxidation time when it was approximately reduced by a few micrometers. This new double-sided anodic alumina membrane can be used as the high-quality functional field emission materials and templates.