Melt Foaming Process Research Articles

Effect of Ultrasonic Wave on Melt Foaming Process of Aluminum Foam

In this paper the formation and growth of bubbles during the melt foaming process are studied from microcosmic aspect. The forming process of liquid film between two neighboring bubbles is also analyzed. According to the cavity effect of ultrasonic wave, the effect of ultrasonic wave on the fragmentation of cell structures of aluminum foam is investigated. Results show that the effect of ultrasonic wave on the cell structure fragmentation decreases with the increase of the distance from the ultrasonic wave source to the cell structure. Therefore, a new concept, namely aluminum foam of biomimetic gradient structure, is proposed.

A novel method for producing Al-foams and evaluation of their compression behavior

Closed-cell aluminium foams were produced by a melt foaming process using MgCa(CO3)2 (dolomite) as foaming agent. XRD analysis was used to follow the crystallization behaviour of the Al-foam which occurred during the foaming process. The compressive properties of these Al-foams and their deformation behavior were investigated. The structure and the mechanisms of failure were examined by scanning electron microscopy (SEM) supported with an in situ micro-test. Deformation is uniform and strain hardening is observed without a plateau stress. The strength of the Al-foams rises with increasing the relative density. Failure of the foams is mainly attributed to brittle fracture of the cell walls rather than to their plastic buckling leading in this way to a reduced energy absorption ability.

Anisotropic compressive behavior of closed-cell Al–Si alloy foams

The anisotropic compressive behavior of closed-cell Al–Si alloy foams prepared by melt foaming process has been investigated. The results show that the stress drop ratio measured in the longitudinal direction is higher than that in the transverse direction. Moreover, the stress drop ratio decreases with increasing relative density of foamed specimen. The shape anisotropy ratio R increases firstly and decreases afterward with increasing relative density. The Young's modulus ratio and yield stress ratio for closed-cell Al–Si alloy foams were investigated and compared with G&A model. A linear relationship between Young's modulus ratio, yield strength ratio and anisotropy ratio has been obtained. The Young's modulus is more sensitive to cell shape than yield stress.

The compressive properties of closed-cell Zn-22Al foams

The closed-cell Zn-22Al (ZA22) foams were fabricated by the melt foaming process using CaCO3 blowing agent. The compressive properties of ZA22 foams were investigated under quasi-static condition. The results show that the compressive stress–strain curves of ZA22 foams exhibit three distinct deformation regions: a linear elastic region where the stress rises linearly with increasing strain; a plastic plateau region with slight stress fluctuation over a wide range of the strain; and a densification region where the stress increases rapidly. The plastic collapse stress of ZA22 foams rises with increasing relative density. The relationship between relative plastic collapse stress and relative density is in accordance with Gibson and Ashby model.

Effect of decomposition properties of titanium hydride on the foaming process and pore structures of Al alloy melt foam

The Al alloy foam was prepared by melt foaming method with addition of titanium hydride as blowing agent. The effects of thermal decomposition properties of titanium hydride on Al alloy melt foaming behavior and pore structures were studied. The decomposition properties of titanium hydride powder were investigated by using temperature programmed decomposition (TPD) set-up. By separating and simulating the TPD spectrum of titanium hydride, a set of thermal decomposition kinetics equations of titanium hydride were acquired. Combining these equations with researches by using instant freezing method, scanning method and real-time method for measuring melt pore structure, the relationship between Al alloy melt foaming process and decomposition properties of titanium hydride was revealed, according to which the Al alloy foam with different pore structures were successfully prepared.

The relationship between thermal decomposition properties of titanium hydride and the Al alloy melt foaming process

Using a new temperature programmed decomposition (TPD) theory and related experimental technique, a set of thermal decomposition kinetics equations of titanium hydride can be acquired by separating and simulating its TPD spectrum. According to these equations, the relation curve of decomposition quantity and time for titanium hydride at temperature of 940 K is obtained and the result coincides well with the Al alloy melt foaming process, which provides a scientific basis for controlling the Al alloy melt foam and then the Al alloy foams with different pore structure are successfully prepared.

Thermal decomposition kinetics of titanium hydride and Al alloy melt foaming process

A temperature programmed decomposition (TPD) apparatus with metal tube structure, in which Ar is used as the carrier gas, is established and the TPD spectrum of titanium hydride is acquired. Using consulting table method (CTM), spectrum superposition method (SSM) and differential spectrum technique, TPD spectrum of titanium hydride is separated and a set of thermal decomposition kinetics equations are acquired. According to these equations, the relationship between decomposition quantity and time for titanium hydride at the temperature of 940 K is obtained and the result well coincides with the Al alloy melt foaming process.

Effects of process parameters and alloy compositions on the pore structure of foamed aluminum

A study was carried out to understand the dependence of the structures of foamed aluminum (FA) on the process variables and to seek an effective measure to overcome the difficulties in preparation of FA by melt foaming process. The following variables were examined: thickening-stirring time, addition of thickening agent, foaming temperature, addition of foaming agent, and the solidification behavior of the alloy. It was found that the slurry viscosity and foaming temperature have very strong effects on the density of FA. Selecting a suitable thickening agent for a required density is very important. Excessive high foaming temperature would result in unnecessarily large pores and non-uniform distribution. It may become easier to obtain a uniform pore distribution if selecting an alloy that has a wider solidification range.

Effects of viscosity on cellular structure of foamed aluminum in foaming process

The effects of melt viscosity on the foaming process and the structures of foamed aluminum have been examined. Methods for measuring the melt viscosity, pore structure, and foaming process are introduced. To increase the stability of the foaming melt and get the sample with a uniform pore distribution, a proper viscosity is needed. Further, the structure of foamed aluminum can be controlled by adjusting the Ca addition and other process parameters.