raised to 645
C (Æ2
C) which corresponds to a net fraction between 75% and 85%, maintained for 60 s, and then the whole
set was taken to a hydraulic press for the infiltration of aluminum in the ceramic balloons as shown in the schematic diagram.
The maximum stress generated by the press for the infiltration was 3.25 MPa.
The preparation of the samples for metallurgical analysis consisted of cutting and filling them in resin, sanded using silicon
carbide (SiC) sandpaper in the 200, 400, 600, 800, 1200 and 1500 grades, using water as a lubricant. After sanding, the
samples were polished with alumina paste with 6 μm granulometry and with diamond paste with 1 μm granulometry for
finishing, being lubricated with ethyl alcohol.
Samples in the form of sandwich panels with syntactic foam, were also subjected to uniaxial quasi-static compression tests
on a universal testing machine with a continuous advance rate of 5 mm/min. In this sense, the samples were machined in a
parallelepiped format with average measurements of 9 Â 9 Â 14 mm, with the AMSF layer in the lower half of the sample.
For findings regarding the distribution of balloons in the matrix, measurement of the metallic walls that separate them and
evaluation of infiltration defects, computerized x-ray microtomography analyzes were performed. The images were generated
by the 360
rotation of cubic samples with a 10 mm edge, with a 0.6
rotation step between each frame and an exposure of
1158 ms. The report was generated by the CTAn software at CNPEM (National Nanotechnology Laboratory) in Brazil.
4.3 Results and Discussions
During the compression tests of the samples containing an upper layer of solid aluminum and a lower one composed by
AMSF, it was noted that this second layer suffered greater deformation compared to the first. The results showed macroscopic
deformations in both layers. Therefore, in this topic the way in which the foam layer collapsed on a macroscopic and
microscopic scale will be analyzed. In order for the phenomenon of structural collapse of balloons and metallic walls of
AMSF to be understood, SEM and Micro CT analyzes were performed on samples of this foam with three deformation
percentages.
A characteristic behavior of metal foams under compressive deformation can be observed in the curve of the sandwich
panels shown in Fig. 4.2. Therefore, the curve begins and develops through a region of proportionality that represents the
elastic phase of the composite, where the structural integrity of the balloons is maintained. Then, once the point known as
offset stress is overcome, the foam enters another regime and begins to deform plastically in three possible ways, in the case of
the foam developed in this work:
If the balloons are less resistant than the metal wall, they collapse and make room for the new and necessary accommodation of the material, due to the advance of the deformations.
Fig. 4.1 SEM analysis of the Fly Ash balloons
4 Compressive Behavior of AlSiMg0.5Mn Matrix Syntactic Foam Produced. . .
21
C (Æ2
C) which corresponds to a net fraction between 75% and 85%, maintained for 60 s, and then the whole
set was taken to a hydraulic press for the infiltration of aluminum in the ceramic balloons as shown in the schematic diagram.
The maximum stress generated by the press for the infiltration was 3.25 MPa.
The preparation of the samples for metallurgical analysis consisted of cutting and filling them in resin, sanded using silicon
carbide (SiC) sandpaper in the 200, 400, 600, 800, 1200 and 1500 grades, using water as a lubricant. After sanding, the
samples were polished with alumina paste with 6 μm granulometry and with diamond paste with 1 μm granulometry for
finishing, being lubricated with ethyl alcohol.
Samples in the form of sandwich panels with syntactic foam, were also subjected to uniaxial quasi-static compression tests
on a universal testing machine with a continuous advance rate of 5 mm/min. In this sense, the samples were machined in a
parallelepiped format with average measurements of 9 Â 9 Â 14 mm, with the AMSF layer in the lower half of the sample.
For findings regarding the distribution of balloons in the matrix, measurement of the metallic walls that separate them and
evaluation of infiltration defects, computerized x-ray microtomography analyzes were performed. The images were generated
by the 360
rotation of cubic samples with a 10 mm edge, with a 0.6
rotation step between each frame and an exposure of
1158 ms. The report was generated by the CTAn software at CNPEM (National Nanotechnology Laboratory) in Brazil.
4.3 Results and Discussions
During the compression tests of the samples containing an upper layer of solid aluminum and a lower one composed by
AMSF, it was noted that this second layer suffered greater deformation compared to the first. The results showed macroscopic
deformations in both layers. Therefore, in this topic the way in which the foam layer collapsed on a macroscopic and
microscopic scale will be analyzed. In order for the phenomenon of structural collapse of balloons and metallic walls of
AMSF to be understood, SEM and Micro CT analyzes were performed on samples of this foam with three deformation
percentages.
A characteristic behavior of metal foams under compressive deformation can be observed in the curve of the sandwich
panels shown in Fig. 4.2. Therefore, the curve begins and develops through a region of proportionality that represents the
elastic phase of the composite, where the structural integrity of the balloons is maintained. Then, once the point known as
offset stress is overcome, the foam enters another regime and begins to deform plastically in three possible ways, in the case of
the foam developed in this work:
If the balloons are less resistant than the metal wall, they collapse and make room for the new and necessary accommodation of the material, due to the advance of the deformations.
Fig. 4.1 SEM analysis of the Fly Ash balloons
4 Compressive Behavior of AlSiMg0.5Mn Matrix Syntactic Foam Produced. . .
21