Nanoindentation sample preparation for Al

The following is an SOP for the preparation of cast aluminum alloys samples for nanoindentation testing.

Loss Prevention

• Safety glasses are required to work in polishing labs at Michigan Technological University.
• Be mindful of the polishing machines. There are pinch points when moving the head and the grinding pads could cause abrasions.
• The air hose in the polishing lab is strictly for drying samples.
• EDM produces Ozone- keep machine closed during operation

Procedure

1. Mark part with a marker where future cuts will be made

Figure 1. Autopolisher in Polishing Lab

1. Cut samples from part using edm (electrical discharge machining) to minimize subsurface deformations
   • Cutting settings
     • Current 3A
     • Voltage 4kV biased voltage
     • Feed rate .4mm per minute (speed through material)
     • Enter code (Gcode) to determine cut
2. Mount the samples
   • See Sample Epoxy Mounting SOP
3. Grind the testing surface manually using 600-grit SiC paper (Hudson)
   • When the marking is gone, the epoxy layer should be removed (Roughly 5 minutes)
   • Lubricate disk with water
4. Grind the testing surface using 800-grit SiC paper (Hudson)
   • Polish for 2 minutes with a pressure of 20N or 5lb
   • Lubricate disk with water
5. Grind the surface using 1200-grit SiC paper (Hudson) using an auto-polisher(shown in figure 1) for 3 minutes with 20N load
   • Fully load the auto polisher (3 samples) to maintain an even force on the samples
   • Lubricate disk with water
6. Polish samples with 3μm diamond paste polish for 10 minutes with a 20N load on a disc reserved for this purpose.
   • Use Red lube to lubricate the disk. Do not use water.
   • To apply diamond paste, Rub the paste into the disk with a gloved fingertip while the wheel spins around 100-200RPM.

Figure 2. A380 aluminum with .05um polish under 100X magnification

1. Polish samples with 1μm diamond paste polish for 10 minutes with a 20N load on a different disc reserved for this purpose.
   • Use Red lube to lubricate the disk. Do not use water.
   • To apply diamond paste, Rub the paste into the disk with a gloved fingertip while the wheel spins around 100-200RPM.
2. Polish samples with .05μm Aluminum oxide polish for 5 minutes with a 40N load on a disc reserved for this purpose.
3. Inspect surface under an optical microscope to ensure that the surface is well polished.
   • For nanoindenation, the testing area should be smooth under 100X magnification
   • If surface is too damaged, It needs to be resurfaced starting with the 600 grit paper