The common problem with aluminum alloy metallographic analysis is not "invisible tissue", but rather tissue masked by scratches, deformed layers, excessive corrosion, or polished contamination. The hardness of the aluminum alloy is relatively low, and the response of the silicon phase, the second phase and the substrate during the sample preparation process is significantly different. The same set of polishing parameters are directly applied to all aluminum alloy grades, and stable results are often not obtained.
The aluminum matrix is softer and prone to scratches and embedded abrasives; eutectic silicon, primary silicon, or intermetallic compounds are harder and prone to bumps, tailing, and edge peeling. When the cutting stress is too large, the surface layer may be deformed or even remelted locally, and the observed tissue is no longer the original state of the material.
The sampling position should correspond to the test purpose. When observing the as-cast microstructure, it is necessary to distinguish between the surface layer, the center and the hot joint area; when checking the extrusion, rolling or forging microstructure, the sampling direction and the machining direction should be recorded; when analyzing the failure parts, the crack source, the extension area and the normal area should be included.
When cutting, select the cutting blade suitable for aluminum alloy to reduce the feed rate and ensure adequate cooling. Thin-walled profiles, foils and small pieces require the use of clamps or inlay supports and cannot be forcibly cut in a free state.
When it is necessary to observe the edges, plating, oxide film or fine second phase, it is recommended to use a mosaic material close to the hardness of the aluminum matrix to avoid excessive rounding of the edges. Cold mounting is more suitable for heat-sensitive materials, and hot mounting should ensure that the temperature does not change the tissue.
Corrosion systems such as Keller reagents are commonly used for aluminum and aluminum alloys, but the grade, heat treatment state, silicon content, and detection purpose are different, and the ratio and time will be different. It is recommended to test for a short period of time to confirm the display effect of the grain boundary, matrix and second phase under a microscope, and then adjust it step by step.
The bright field is suitable for observing the matrix, grain boundaries, second phase, pores, and inclusions; the polarized or dark field can help to distinguish between partial phase and tissue boundaries. If grain sizes or proportions need to be assessed, calibrated cameras and image analysis software should be used with fixed magnification, illumination and corrosion conditions.
JM435 Upright metallographic microscope can be used to observe the microstructure, grains and second phase of aluminum alloy
Conventional aluminum alloy microstructure analysis can be configured with 5X, 10x, 20x, 50x brightfield objectives, and polarized or darkfields can be added as needed. If grain size, second ratio and defect size need to be measured at the same time, camera resolution, software calibration and reporting functions should be prioritized.
Related Columns: Metallographic Microscope, Metallographic Sampling Equipment. You can also refer to the JM435 Upright Metallographic Microscope.
The aluminum alloy test report shall retain the material grade, status, sampling direction, corrosion conditions and original image. The grain size, second phase area and pore size should have a clear statistical area to avoid taking only the most representative small pieces of the picture.
If some samples of the same batch of materials have clear tissue and some samples are all scratches, differences should be found from the cutting and polishing process first, rather than forcing image improvement through software sharpening.
Submit aluminum grades, status and observation targets for sample preparation and microscope configuration recommendations
Tell us the material, the feature you need to see and the magnification range. We will recommend a configuration and quote it.
