Melt Foaming Process Research Articles

Bi-continuous interpenetrated porous composite integrating the high strength and long plateau stress stage prepared by an in situ method

In this paper, bi-continuous interpenetrated porous composites (BIPCs) were prepared with the combination of melt foaming and infiltration casting process. All BIPCs exhibited superior mechanical performance than aluminum foam (AF) and the sum of their components. Among them, 4# BIPC (with 75 struts) showed the highest specific energy absorption which is 2.70 times that of AF, and 3# BIPC (with 48 struts) presented the best improvement in terms of structural strength, while 2# BIPC (with 27 struts) exhibited the largest enhancement of energy absorption. The results indicate that the in situ interface of AF and ordered lattice structure contributes to the enhanced strength of BIPCs, while pores in AF prolongs the stress plateau stage. This research provides a novelty method to solve the trade-off between different mechanical property indicators.

Investigating Alumina-Silicate Bauxite and Phenol-Formaldehyde Resin Embedded TiH2 as Foaming Agents for Producing A356 Foam

The melt foaming process has become the most widely used method in closed-cell aluminum foam manufacturing in large dimensions. This process creates pores by adding a foaming agent to the molten metal. Therefore, selecting appropriate foaming agents is vital, and it controls pore sizes and their distribution in producing a homogeneous foam. In the current research, as cost-effective foaming agents, the Bauxite and Phenol-formaldehyde resin (PFR) embedded TiH2 were successfully produced and then investigated by SEM and EDX analysis. It can be concluded that in the presence of the Bauxite ceramic phase and silica gel formation in Bauxite-embedded TiH2 and the formation of a carbon layer due to the burning of resin in PFR-embedded TiH2, heat-resistant protective layers are formed around TiH2 powders, and thus it delays (120 s) the gas release. The delay in the decomposition of H2 gas is equal to/higher than in the literature, and it gives the gas’ bubbles enough time to establish pores in the metallic matrix; thus, foams with uniform distribution of pores were produced. A quantitative examination of the cross-section of the produced foams shows that the number of cells with smaller sizes in the foams produced with the modified foaming agent is more, and the distribution of pores or cells is more homogeneous.

Accurate determination of bubble size and expansion ratio for polymer foaming with non-isothermal PBB model based on additional energy conservation

A non-isothermal pressure-balanced bubble-growth (PBB) model has been proposed based on mass, momentum and energy conservation, which additionally considered the decrease in the internal energy of gas due to the work done by gas expansion in bubble. The model could accurately predict the bubble size and expansion ratio for the melt foaming of four polymers for a wide range of cell densities from 1.5 × 1013 to 1.9 × 1015 cells/m3. Furthermore, the simulation results indicate that the bubble shell resisted bubble growth and consumed significant energy, preventing the growth of some small nucleations. During the melt foaming process, the energy cost of the linear polymer is continuously kept at a high level, which reduces the bubble size, while that of the long-chain branched polymer attenuates fast, thereby increasing the expansion ratio. Finally, we defined the gas efficiency of the foaming agent to evaluate the economic feasibility of the foaming agent in foaming processes.

Development of AlMg35-TiH2 composite foaming agent and fabrication of small pore size aluminium foams

Abstract In the melt foaming process of aluminium foams, small pore size aluminium foam is difficult to fabricate, this is mainly due to the early decomposition and poor dispersion of foaming agent (usually TiH2). In this study, these two problems are solved concurrently by introducing a TiH2-AlMg35 composite foaming agent in the melt foaming process. The composite foaming agent was fabricated by premixing the foaming agent (oxidizing treated TiH2) into a low melting point master alloy (AlMg35) melt. Microstructure and particulate distribution of the composite foaming agent were examined. Suitable dispersing parameters were obtained. Aluminium foams, with small pore size, better porous structure uniformity and good process controllability were fabricated using the TiH2-AlMg35 composite foaming agent. Average pore size reached as small as 0.6mm. This process has a simple procedure, low cost, and is suitable for commercial production.

Examination of the Thickening Effect of Hollow Ceramics during Porous Aluminum Production by Melt Foaming Process

Examination of the Thickening Effect of Hollow Ceramics during Porous Aluminum Production by Melt Foaming Process

Determination of modified polyamide 6's foaming windows by bubble growth simulations based on rheological measurements

ABSTRACTReactive extrusion was used to modify virgin polyamides 6 (v‐PA6) and to prepare chain extended PA6 (CE‐PA6) and long‐chain branched PA6 (LCB‐PA6) for the melt foaming process. This was done using a twin‐screw extruder and the following modifiers: a chain extender ADR‐4368 and a branching agent maleic anhydride grafted polypropylene. A reaction mechanism was proposed to explain the chain extension and long‐chain branching reactions and was verified by the Fourier transform infrared spectroscopy data. The analysis of the gel permeation chromatography data showed that LCB‐PA6 presented a strong increase in the molecular weight and in the dispersity index. Moreover, the rheological properties of the v‐PA6 and modified PA6 resins were characterized by a dynamic shear test. The LCB‐PA6 compared with CE‐PA6 showed much higher shear viscosity and longer characteristic relaxation times, indicating the presence of an LCB structure. A uniaxial elongation test showed that the LCB‐PA6 had the highest melt viscosity and melt strength as well as most obvious strain‐hardening behavior. A high‐pressure differential scanning calorimeter under compressed CO2 was used to investigate the PA6's crystallization properties so as to analyze its minimum temperature of foaming windows. The melt foamability of the CE‐PA6 and the LCB‐PA6 was verified by batch melt foaming experiments with CO2 as the blowing agent and maximum temperature of foaming windows was also quantitatively determined by numerical simulation of bubble growth based on the rheological measurements. The results showed that the LCB‐PA6 foams had a smaller cell diameter, a larger cell density, a greater expansion ratio, and wider foaming temperature window than the CE‐PA6. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48138.

Magnesium-Based Foam Biomaterials and their Related Properties

The magnesium-based foam biomaterials were prepared by melt foaming process, where Mg-Ca alloy was used as matrix material, hydroxyapatite (HA) as tackifier, MgCO3as foaming agent. The magnesium-based foam biomaterials with uniform structure were used for testing to investigate their compressive and biodegradable behaviors. The biodegradable property of the magnesium-based foam was mainly characterized by microstructure observation and hydrogen evolution. The results showed that the porosity of the magnesium-based foam has a more important impact on yield stress and plateau stress of compressive curves compared to HA content or its size. Corrosion rate of the magnesium-based foams decreases with increasing HA addition. Meanwhile, the porosity of the magnesium-based foams also has a very obvious effect on hydrogen evolution, i.e., the hydrogen evolution rate increases with decreasing the porosity of magnesium-based foams.

Research on Dynamic Accumulation Effect and Constitutive Model of Aluminum Foams Under Dynamic Impact

Aluminum foams were prepared by melt foaming process. The mechanical properties of aluminum foams under repeated impacts were studied. The porosity and pore size of the prepared aluminum foam were measured. The effects of damage accumulation on the failure morphology of aluminum foam, the transmission rate, stress–strain curve, energy absorption capacity, and the ideal energy absorption efficiency were analyzed. The influence of the number of impacts on the dynamic mechanical properties of the material under the condition of equivalent damage accumulation was studied. Based on the Sherwood–Frost equation, the damage cumulative constitutive model of the aluminum foams under repeated impacts was established. The influence of the difference between the damage cumulative energy corresponding to the reference curve of the shape function and the damage cumulative energy in multiple impacts tests on the prediction accuracy of the constitutive model was analyzed. The results show that with the increase in the number of impacts, the degree of damage to aluminum foam increases, transmission rate increases, the elastic limit stress and the corresponding strain are enhanced, and the damage accumulation effect on aluminum foam under repeated impacts is helpful to improve the ideal energy absorption efficiency. It is verified that the constitutive model can reflect the mechanical properties of aluminum foam under repeated impacts.

Energy Absorption of Superplastic Zn-22Al Alloy Foam Manufactured through Melt Foaming Process

Closed-cell superplastic Zn-22Al alloy foams were manufactured through the melt foaming process using sodium hydrogen carbonate powder as a foaming agent. Foaming tests were carried out under different foaming temperatures, times and additive amounts of foaming agent. The porosity of Zn-22Al alloy foams were between 30 and 70%. The cell wall consisted of fine equiaxial crystal grains after solution treatment. The compressive properties of the Zn-22Al alloy foams were investigated at room temperature and high temperature. Zn-22Al alloy foams exhibited high strain rate sensitivity, which was caused by superplastic deformation of the cell wall material.

Effect of Decomposition Kinetics of Titanium Hydride on the Al Alloy Melt Foaming Process

The gas released from the titanium hydride decomposition is one of the key factors to influence the Al alloy melt foaming process. In this study, a set of decomposition kinetic equations of titanium hydride was acquired by separating its temperature programmed decomposition (TPD) spectrum, which was acquired by a special designed TPD apparatus with argon used as carrier gas and thermal conductivity cell as the detector. According to these equations, the decomposition and hydrogen release characteristics of titanium hydride at a fixed/elevated temperature are described quantitatively, which can be applied to forecast the Al alloy melt foaming process and furnish the theoretical basis for fabrication of three-dimensional complex shaped Al alloy foam.

Compressive behavior of Zn–22Al closed-cell foams under uniaxial quasi-static loading

Zn–22Al alloy closed-cell foams were fabricated by melt foaming process using hydride foaming agent. The compressive properties were investigated under quasi-static condition. The structure of the foamed material was analyzed during compression test to reveal the relationship between morphology and compressive behavior. The results show that the stress–strain behavior is typical of closed-cell metal foams and mostly of brittle type. Governing deformation mechanism at plateau stage is identified to be brittle crushing. A substantial increase in compressive strength of Zn–22Al foams was obtained. The agreement between compressive properties and Gibson–Ashby model was also detected.

Melt foamability of reactive extrusion‐modified poly(ethylene terephthalate) with pyromellitic dianhydride using supercritical carbon dioxide as blowing agent

By reactive extrusion with pyromellitic dianhydride (PMDA), foamable poly(ethylene terephthalate) (PET) was obtained, which achieved a maximum intrinsic viscosity of 1.36 dL/g with PMDA content 0.8 wt%. Dynamic shear rheological properties were measured to characterize the structure evolution of modified PET. And the Avrami analysis was extended for the non‐isothermal crystallization process of modified PET, which relates to cell stabilization in the melt foaming process. Based on the batch foaming process with supercritical carbon dioxide as blowing agent, broad foaming temperature windows were obtained for PETs modified with 0.8 and 0.5 wt% PMDA, in which PET foams with the expansion ratio between 10 and 50 times, the cell diameter between 15 and 37 μm, and the cell density between 6.2 × 108 and 1.6 × 109 cells/cm3 were controllably produced. POLYM. ENG. SCI., 55:1528–1535, 2015. © 2014 Society of Plastics Engineers

Comparison of Cell Wall Microstructure of Aluminum Foams Produced by Melt Foaming and Gas Injection Foaming Processes

Aluminum foams from A356 base alloy were produced by both the melt foaming process and gas injection foaming process. A comparison of microstructures between the two kinds of aluminum foams was carried out. The related causes were analyzed to form the difference in microstructure. Results indicate that aluminum foams produced by different processes are distinct in metallurgical structure. The average thickness of cell wall, the species and area fraction of secondary phases or particles and other metallurgical features have been all comparatively studied. The difference in microstructure features of the cell walls will also make the aluminum foams different in mechanical properties. Therefore, we need to select proper foaming process for aluminum foams according to the property requirements in practical application.

溶湯発泡法で作製されたポーラス Zn-22Al 超塑性合金のセル形態に及ぼす発泡条件の影響

Closed-cell superplastic Zn-22Al eutectoid alloy foams were manufactured through the melt foaming process using titanium hydride powder as a foaming agent. Foaming tests were carried out under different foaming temperatures, times and additive amounts of foaming agent. Maximum porosity of 75% and small pore diameter were obtained during the temperature range of semi-solid condition from 738-753 K. This is because of increased melt viscosity. Though the small amount of the foaming agent is effective to decrease the pore diameter, the porosity becomes low. Cell morphology of the present Zn-22Al alloy foam is identical to conventional aluminum foams. Semi-solid condition of Zn-22Al foam has an advantage over increasing melt viscosity on manufacturing of metal foam.

Effect of Porosity on Tensile and Compressive Deformations of Superplastic Zn-22Al Alloy Foam

Closed-cell Zn-22Al superplastic alloy foams were manufactured through the melt foaming process. The Zn-22Al foams were produced with varying porosity of 51-71%. The tensile and compressive properties of the Zn-22Al foams were investigated at 523 K. The compressive specimen has m-value of 0.55 in the low strain rate region. This is because of the superplastic deformation induced by the fine microstructure of the cell wall. Though the superplastic elongation was not obtained in high temperature tensile test, the elongation was higher than that of conventional aluminum foams.

Closed-cell Al alloy composite foams: Production and characterization

Foamy Al alloy SiCp composites of different densities ranging from 0.4 to 0.7g/cm3 were manufactured by melt-foaming process, which consisted of direct CaCO3 addition into the molten A356 aluminum bath. Mechanical properties and morphological observations indicated that the three-stage deformation mechanism of typical cellular foams is dominant in the produced A356 aluminum foams. Middle-stage stress plateau shrinkage plus compressive strength and bending stress enhancements were observed in denser foams. With the same Al/SiCp ratio, energy absorption ability and plastic collapse strength of the closed-cell foams were increased with the foam density. Doubling cell-face bending effects resulted in larger compressive than bending strengths in the closed-cell foams; while stiffness lowering was due to the cell-face stretching conditions.

Solidification Structure and Sound Absorbability of A356 Alloy Foams

Metallic foams of A356 alloy with a uniform porosity of 75-85% were produced with the melt foaming process. The microstructure inside the foam cell walls was experimentally studied. It is found that the microstructure is greatly different from the as-cast structure of the base alloy. It is believed that the thickening process with calcium, the adding of foaming agent and the mixing process during the production process all play important roles on the solidification microstructure of the cell walls. The morphology and grain size of primary α-phase, the amount and morphology of eutectic silicon, the distribution and size of CaSi2Al2 and residual titanium hydride particles were studied. The sound absorption coefficient of the alloy foams was measured. Two methods, drilling small holes and compressing the foam, have been developed to improve the sound absorbability of the alloy foam in low and middle frequency ranges.

Deformation and energy absorption characteristic of Al 2O 3f/Zn–Al composite foams during compression

In this study, Zn–Al matrix composite foams reinforced with Al 2O 3 short fibers (Al 2O 3f/Zn–Al composite foams) were fabricated with the melt foaming process. The compressive properties and the energy absorption characteristics of the composite foams were investigated. To obtain the failure behaviour, the deformation of the composite foams was observed by scanning electron microscope (SEM). The results show that the microstructures of the foams have a significant effect on the compressive behavior of the composite foams. The strengthen mechanisms of the fiber on compressive properties of the composite foams were presented. Furthermore, the composite foams exhibit a high energy absorption characteristic.

Energy Absorption Capability of Zn-22Al Superplastic Alloy Foam Manufactured through Melt Foaming Process

Energy Absorption Capability of Zn-22Al Superplastic Alloy Foam Manufactured through Melt Foaming Process

Energy Absorption Capability of Zn-22Al Superplastic Alloy Foam Manufactured through Melt Foaming Process

Superplastic Zn-22Al alloy foams were manufactured through the melt foaming process using titanium hydride powder as a foaming agent. The compressive properties of the Zn-22Al foams were investigated under quasi-static and dynamic loading conditions. Experimental results show that the flow stress and the energy absorption of the Zn-22Al foam significantly increased with increasing the strain rate. At high strain rate region, the energy absorption of the Zn-22Al foams is also larger than that of conventional aluminum foams. These behaviors are due to superplastic deformation of cell walls.