Tensile Properties and Fracture Behavior of Aluminum Alloy Foam Fabricated from Die Castings without Using Blowing Agent by Friction Stir Processing Route

Tensile Behavior and Performance of Syntactic Steel Foams Prepared by Infiltration Casting

Syntactic steel foams (SSFs) were prepared by low-pressure infiltration of molten ASTM CF-8 cast austenitic stainless steel into randomly and densely packed Al2O3 hollow spheres. The microstructure of the SSFs was characterized by scanning electron microscopy and energy dispersive spectrometry. Using dumbbell-shaped specimens, the density of the as-cast SSFs is measured in the range from 3.33 to 3.64 g/cm3 and their ultimate tensile strength from 83.1 to 97.6 MPa. No significant chemical reaction was detected between the fillers and matrix. The quasi-static uniaxial tensile deformation of the syntactic foams underwent elastic deformation, plastic deformation, and then a failure stage, showing similar tensile behavior to plastic bulk metals but different behavior to common metal foams. From the good ductility of the metal matrix, a clear macroscopic plastic deformation was observed before the ductile fracture of the syntactic foams. A constitutive relationship of the SSFs under uniaxial tensile loads has been proposed.

Porosity Defect Remodeling and Tensile Analysis of Cast Steel

Tensile properties on ASTM A216 WCB cast steel with centerline porosity defect were studied with radiographic mapping and finite element remodeling technique. Non-linear elastic and plastic behaviors dependent on porosity were mathematically described by relevant equation sets. According to the ASTM E8 tensile test standard, matrix and defect specimens were machined into two categories by two types of height. After applying radiographic inspection, defect morphologies were mapped to the mid-sections of the finite element models and the porosity fraction fields had been generated with interpolation method. ABAQUS input parameters were confirmed by trial simulations to the matrix specimen and comparison with experimental outcomes. Fine agreements of the result curves between simulations and experiments could be observed, and predicted positions of the tensile fracture were found to be in accordance with the tests. Chord modulus was used to obtain the equivalent elastic stiffness because of the non-linear features. The results showed that elongation was the most influenced term to the defect cast steel, compared with elastic stiffness and yield stress. Additional visual explanations on the tensile fracture caused by void propagation were also given by the result contours at different mechanical stages, including distributions of Mises stress and plastic strain.

Fabrication of Aluminum Tubes Filled with Aluminum Alloy Foam by Friction Welding

Aluminum foam is usually used as the core of composite materials by combining it with dense materials, such as in Al foam core sandwich panels and Al-foam-filled tubes, owing to its low tensile and bending strengths. In this study, all-Al foam-filled tubes consisting of ADC12 Al-Si-Cu die-cast aluminum alloy foam and a dense A1050 commercially pure Al tube with metal bonding were fabricated by friction welding. First, it was found that the ADC12 precursor was firmly bonded throughout the inner wall of the A1050 tube without a gap between the precursor and the tube by friction welding. No deformation of the tube or foaming of the precursor was observed during the friction welding. Next, it was shown that by heat treatment of an ADC12-precursor-bonded A1050 tube, gases generated by the decomposition of the blowing agent expand the softened ADC12 to produce the ADC12 foam interior of the dense A1050 tube. A holding time during the foaming process of approximately t_H = 8.5 min with a holding temperature of 948 K was found to be suitable for obtaining a sound ADC12-foam-filled A1050 tube with sufficient foaming, almost uniform pore structures over the entire specimen, and no deformation and minimum reduction in the thickness of the tube.