C95400 Aluminum Bronze

Use slow-speed diamond saw or abrasive cut-off wheel designed for non-ferrous materials. Standard cut-off wheel (1.0-1.5 mm thickness) is appropriate. Use adequate coolant flow to prevent overheating and minimize deformation. Cutting speed: 150-250 RPM for most cut-off saws. Apply steady, moderate pressure - the material allows for reasonable feed rates. Avoid forcing the cut which can cause wheel wear and sample damage. Leave adequate allowance (~2-3 mm) for grinding away the heat-affected zone from cutting.

Cold mounting with epoxy resin is preferred to avoid heat that could affect the microstructure. Use a low-shrinkage epoxy resin for best edge retention. Ensure complete cure before grinding to prevent edge rounding and maintain sample integrity.

Hot compression mounting is acceptable if the part tolerates ~150-180°C and moderate pressure (2000-3000 psi for phenolic). Use phenolic or epoxy-phenolic resins. Ensure proper cooling under pressure to minimize shrinkage.

The medium hardness (170 HB) of C95400 Aluminum Bronze requires careful grinding. Use standard SiC grinding papers with adequate water lubrication. Disc speed: 200-300 RPM. Apply light to moderate pressure (25-35 N per 30 mm sample) - avoid excessive force that could cause work hardening. Use sharp, fresh grinding papers to minimize deformation.

Grinding sequence:

• 240 grit: Remove sectioning damage (30-60 seconds). Use moderate pressure to remove heat-affected zone.
• 320 grit: Remove previous scratches (30-60 seconds). Ensure complete scratch removal.
• 400 grit: Remove previous scratches (30-60 seconds). Ensure complete scratch removal.
• 600 grit: Remove previous scratches (30-60 seconds). Ensure complete scratch removal.

Always rotate the specimen holder 90° between steps to ensure complete scratch removal. Use complementary rotation (platen and holder same direction, different speeds) rather than contra-rotation to minimize deformation. Adequate water lubrication is critical - avoid drying during grinding which can cause smearing.

The medium hardness requires careful polishing. Use diamond polishing with appropriate polishing pads for each stage. Apply light to moderate pressure throughout to prevent deformation.

Diamond polishing sequence:

• 6μm diamond: 2-4 minutes on a medium-hard synthetic pad (e.g., TEXPAN) with light to moderate pressure (25-35 N per 30 mm sample). Start with 6μm to minimize damage. ensure complete scratch removal at each step.
• 1μm diamond: 2-4 minutes on a medium-hard synthetic pad (e.g., TEXPAN) with light pressure (20-30 N). Continue removing scratches from previous step.
• 0.05μm colloidal silica: 1-2 minutes on a high-napped final polishing pad (e.g., MICROPAD) with very light pressure. This removes any remaining fine scratches and prepares the surface for etching. Monitor for relief - reduce polishing time if excessive relief develops.

Use appropriate polishing lubricants. The medium material means polishing times should be sufficient but not excessive - avoid over-polishing which can cause relief and affect grain boundary revelation. Monitor the surface frequently under the microscope to check for smearing or excessive relief.

C95400 Aluminum Bronze (Cu-11Al-4Fe) has a microstructure of alpha (Cu-Al solid solution) with kappa phase (Fe₃Al intermetallic) precipitates. Depending on heat treatment, retained beta or transformed beta (martensitic) phases may also be present. The kappa phase distribution is critical for corrosion resistance and mechanical properties. Copper No. 2 (Chemical Etching) — Preferred etchant for aluminum bronzes:

• Composition: 10g FeCl₃ + 50ml HCl (conc.) + 200ml H₂O
• Application: Immerse or swab for 5–15 seconds at room temperature.
• Reveals: Alpha grain boundaries and kappa phase precipitates. FeCl₃ preferentially attacks the alpha matrix, leaving kappa phases in relief. Also reveals any retained or transformed beta phase.
• Rinse: Immediately with water, then ethanol. Dry with compressed air.

Dichromate Etchant (Chemical Etching) — For detailed kappa phase differentiation:

• Composition: 2g K₂Cr₂O₇ + 8ml H₂SO₄ (conc.) + 4ml saturated NaCl solution + 100ml H₂O
• Application: Immerse for 5–20 seconds at room temperature.
• Reveals: Excellent contrast between kappa phase variants and the alpha matrix. Useful for assessing heat treatment effectiveness — properly quenched and tempered structures should show fine, well-dispersed kappa precipitates.
• Rinse: Immediately with water, then ethanol. Dry with compressed air.
• Note: Contains hexavalent chromium — use in fume hood with appropriate PPE. Dispose as hazardous waste.

Etching Strategy:

• Start with Copper No. 2 for general microstructure and kappa phase overview
• Use Dichromate Etchant when detailed phase characterization or heat treatment verification is needed
• Use short initial etch times — aluminum bronzes can over-etch quickly
• Iron-rich kappa phases may show slight relief in as-polished condition due to hardness differences

Safety: FeCl₃/HCl generates fumes — use fume hood. Dichromate contains Cr⁶⁺ — handle as hazardous. Wear gloves, safety glasses, and lab coat for all etchants.