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Intermetallic (Ni–Al) foams were fabricated by combustion reactions. The heats of formations of these intermetallics were high enough to obtain bulk reaction products and pores were formed in the specimen during the combustion reaction. Some processing parameters of the combustion reaction were varied to control porosity and cell morphology of the intermetallic foams. The amount of aluminum in the green compact was an important factor in controlling the porosity of the synthesized nickel aluminide. The relative density of the green compact needed to be more than 0.72 for effective foam formation. The enthalpy change of the combustion reaction was controlled either by adding a reaction‐ enhancing agent (B4C) or by adding a heat‐absorbing agent (TiC). Both the porosity and the cell size of the synthesized intermetallics were successfully controlled by changing the reaction enthalpy (from 10 to 85 % porosity).

Since the aluminum foam has the unique structure of containing many cells inside, it shows the unique feature as shown below. -Lightweight (relative density: < 1.0) -High rigidity compared with the same material of the same weight -High energy absorption -Low thermal conductivity -High damping capacity -Gas permeability (when the cell structure is open)The aluminum foam, therefore, is expected widely applied to future industrial products.One of the techniques of manufacturing the aluminum foam is a precursor method which uses the blowing agent (titanium hydride: TiH 2 ). By this precursor method, the precursor is made from mixture of aluminum powder and appropriate quantity of foaming agent. The precursor is generally produced by hot pressing, hot extrusion or other compacting processes. When the precursor is heated, the foaming agent decomposes and pores are formed in molten aluminum, which results in the formation of the aluminum foam.This manufacturing technique has the advantage of the possibility for producing near-net-shape components of foams by foaming in the mold and integrated cladding components by foaming and filling in hollow parts. [1][2][3] However, in order to put the aluminum foams in wide industrial use, material and producing costs are still important key issues. [4][5][6] For the cost reduction, it is effective to use recycled machined chip waste instead of aluminum powders to produce foamable precursor. The important issues to produce well foamable precursor from machined chips are firm consolidation of chips and homogeneous dispersion of blowing agent in the precursor. The authors have developed new process to produce foamable precursor from machined chip waste by using compressive torsion processing which is one of severe plastic deformation process. [7] In this process, the chips were subjected to severe shear deformation by simultaneous compression and torsion loading under elevated temperature, and then firm consolidated cylindrical precursor is easily produced from machined chip waste. The aluminum foam made from the chip precursor has similar porosity and pore morphology as that from a powder precursor.In the present work, the production of precursors from different shape and alloy chips and their foaming behavior were investigated. The effects of mixing of different shape chips and different alloy chips were also investigated in the present work. Experimental ProcedureMaterials Different kinds of aluminum alloy machined chips were used in the experiment. To study the effect of the chips shape on the foaming behavior, three kinds of 6063 alloy chips with different types of shape were prepared as shown in Figure 1. Their shapes are quite different from thin chips to long string type waste. To study the effect of alloy composition, 6063 (Al, Mg:0.45 ∼ 0.9 wt%, Si:0.2 ∼ 0.6 wt%) and 4032 (Al, Si:11.0 ∼ 13.5 wt%, Mg:0.8 ∼ 1.3 wt%, Cu:0.5 ∼ 1.3 wt%, Ni:0.5 ∼ 1.3 wt%) alloy chips with similar shape were pre-COMMUNICATIONS 840

The present study focuses on the investigation of the possibility of producing aluminum foam from low cost machined chip waste. To produce highly porous aluminum, manufacturing process of precursor, the effect of TiH 2 content and the effect of ceramic particle addition were examined. In the study of precursor manufacturing processes, precursors fabricated by extrusion process did not expand sufficiently and the pore morphology was very irregular. In contrast, precursors fabricated by compressive torsion processing satisfactorily expanded and the pore morphology was uniform. There was an adequate range of TiH 2 addition. The increase of TiH 2 content more than 3 mass% was not an effective way to produce highly porous aluminum foam. Addition of fine Al 2 O 3 particle resulted in a significant increase in foam expansion.