Aluminum and aluminum alloys
Metallographic Preparation Solutions by Material
Use this guide for advice on where to start when performing metallographic preparation and analysis on aluminum and aluminum alloys. Included are tips for achieving the best results for your metallographic application.
Things to consider when working with aluminum and aluminum alloys
Depending on the composition, processing and thermal treatment, the preparation method can change. As an example, with pure aluminum, the chances of abrasive particles embedding are higher than with other aluminum materials. A polishing method can be adjusted for this by utilizing paste instead of suspension.
Aluminum Cutting Tips
All sectioning should be performed wet, with an ample flow of coolant directed into the cut. Wet cutting will produce a smoother surface finish than a dry cut. Using coolant will also guard against surface damage caused by overheating and mechanical strains. Reducing damage while sectioning is important. Mechanical damage, such as fractures can penetrate deep into the structure and make later preparation steps longer. There are two main types of cutting tools offered: Abrasive and Precision.
Abrasive Cutting Tips
The size of the abrasive blade also affects cutting parameters. Larger, thicker blades remove more material but also generate more heat than a thinner blade. To reduce the heat produced by blades the feed rates should be lowered.
| Recommended Abrasive blade for Aluminum | |||
|---|---|---|---|
| 10in (254mm) | 12in (305 mm) | 14in (356mm) | 16in (406mm) |
| 102512P 0.06in [1.5mm] | 103012P 0.079in [2mm] | 103512P 0.1 [2.5mm] | 10-31650-010 0.125in [3mm] |
Precision Cutting Tips
Precision cutters are used in metallographic preparation of aluminum when cutting samples that are small or delicate. Precision blades don’t break down as they are being used. On the outer edge of the blade there is a section where abrasive has been bonded with metal alloy and if taken care of one wafering blade can outlast a box of abrasive blades. Wafering blades can be used with aluminum for more difficult cuts including making a precise cut close to a feature of interest, or when it is critical to reduce the width of a cut (kerf loss).
Additional benefits of using a precision cutter are a lower load is applied and consequently, less heat is generated, reducing the amount of damage.
Abrasive blades are also made for precision cutters. They can be used in instances where breaking blades is high. This could be if you have a difficult to clamp part, have a part that might shift during sectioning or you have more variability in the process (ex: multiple operators).
| Recommended Precision blades for Aluminum | |||
|---|---|---|---|
| 5in (127mm) | 7in (178mm) | 8in (203mm) | Dressing Stick |
| 11-4215 0.020in [0.5mm] | 11-4237 0.025in [0.6mm] | 11-4238 0.035in [0.9mm] |
11-1190
11-2490 |
Aluminum Mounting Tips
Mounting samples also protects and preserves edges or surface defects during metallographic preparation. The method of mounting should in no way alter the microstructure of the specimen. Pressure and heat are the most common sources of injurious effects. Temperatures around 350oF and pressures around 4000 PSI are common for hot compression mounting.
Sample geometry and properties can determine the appropriate method for mounting aluminum samples. Use castable mounting when samples are thin or deformed easily. Samples such as these tend to be sensitive to high pressures. If samples are not sensitive to pressure hot compression mounting can be a time and money saver.
For electron microscopy, ProbeMet is a suitable copper-based conductive media. If copper content is of interest in the sample KonductoMet® is a carbon-filled conductive alternative to ProbeMet.
Careful selection can ensure media meets mounting needs regarding timing, viscosity, temperature, and shrinkage. Acrylic systems can increase throughput with quick curing times between 5 -30 minutes. Though quicker in curing, sample adhesion and viscosity of acrylics can sometimes be lacking especially with more intricate shapes. This is where epoxy systems can help. With longer working times, mixed epoxy can be used with a vacuum system to help penetration levels in intricate geometries. Our epoxy systems also offer lower peak exothermic systems. Additional information can be found on our mounting page.
Aluminum Grinding & Polishing Tips for All Methods
Deformation in aluminum and aluminum alloy samples tends to be deeper than in other material types. To help mitigate, swap out SiC papers after 1-minute cycles and keep sequential steps close in abrasive size. Keeping the abrasive sharp will help to reduce the amount of damage created from grinding.
Abrasive particles embedding into aluminum is another possible preparation artifact. If you encounter this problem switch to diamond paste. If using silicon carbide paper then scentless candle wax or paraffin wax can be applied to the paper to help silicon carbide particles from embedding in samples.
Soft aluminum such as o-temper alloys and pure aluminum are susceptible to deformation and scratches, to address this use a brief vibratory polishing step with MasterMet®.
Using Buehler’s Burst Dispensing System can conserve diamond suspension and improve consistency. This system can simultaneously dispense extender and diamond suspension.
The ideal rate for the Burst dispensing system changes with the size of the platen and the polishing cloth that is being used. As a general guideline, for a platen size of 8” a burst setting of 3 is a good starting point, for sizes of 10″ and 12″ set the burst system to 4 and adjust as needed. Some experimentation may be required to determine optimal settings to ensure sufficient abrasive and wetting of the cloth. Burst dispensers are also capable of dispensing extenders simultaneously with diamond suspensions if desired.
Loads listed in grinding and polishing methods are recommendations for one 1.25″ mounted specimen. If using central force during preparation the force listed should be multiplied by the number of samples being polished. For different sample sizes, use our load conversion calculator to determine the correct load for your application.
| Procedure for Grinding and Polishing Aluminum (General) | ||||
|---|---|---|---|---|
| Surface | Loads [N] | Base Speed [rpm] | Relative Rotation | Time |
| CarbiMet® 320 grit | 5 [22] | 300 rpm |
|
Until Plane |
| UltraPad with 9um MetaDi® Supreme Diamond | 5 [22] | 150 rpm |
|
5:00 |
| TriDent with 3um MetaDi Supreme Diamond | 5 [22] | 150 rpm |
|
4:00 |
| ChemoMet® with MasterMet® Colloidal Silica | 5 [22] | 150 rpm |
|
1:30 |
|
= Platen = Specimen Holder *Plus MetaDi Fluid Extender as desired
|
||||
| Procedure for Grinding and Polishing Soft Aluminum including Super Pure Aluminum and Commercially Pure Aluminum | ||||
|---|---|---|---|---|
| Surface | Loads [N] | Base Speed [rpm] | Relative Rotation | Time |
| CarbiMet® 320 grit | 5 [22] | 300 rpm |
|
Until Plane |
| TexMet® C with 9um MetaDi Supreme Diamond | 5 [22] | 150 rpm |
|
5:00 |
| TexMet C with 3um MetaDi Diamond Paste with extender | 5 [22] | 150 rpm |
|
4:00 |
| TexMet C with 1um MetaDi Diamond Paste with extender | 5 [22] | 150 rpm |
|
2:00 |
| ChemoMet with MasterMet Colloidal Silica | 5 [22] | 150 rpm |
|
1:30 |
|
= Platen = Specimen Holder *Plus MetaDi Fluid Extender as desired
|
||||
Aluminum Etching Tips
Aluminum may contain discrete intermetallic particles that may be attacked by etchants before the matrix. If you encounter this problem, energy-dispersive analysis can be used for phase identification in place of etching.
In the table below methods for Aluminum can be found.
| Table 20.1: Light Metals - Aluminum Alloys | |
|---|---|
| Composition | Comments |
| 95mℓ water 2.5mℓ HNO3 1.5mℓ HCl 1.0mℓ HF | Keller’s reagent, very popular general purpose reagent for Al and Al alloys, except high-Si alloys. Immerse sample 10-20 seconds, wash in warm water. Can follow with a dip in conc. HNO3. Outlines all common constituents, reveals grain structure in certain alloys when used by immersion. |
| 90-100mℓ water 0.1-10mℓ HF | General purpose reagent. Attacks FeAl3, other constituents outlined. The 0.5% concentrations of HF is very popular. |
| 84mℓ water 15.5mℓ HNO3 0.5mℓ HF 3g CrO3 | Graff and Sargent’s etchant, for grain sizes of 2XXX, 3XXX, 6XXX, and 7XXX wrought alloys. Immerse specimen 20-60 seconds with mild agitation. |
| 1.8% fluoboric acid in water | Barker’s anodizing method for grain structure. Use 0.5-1.5 A/in2, 30-45 V DC. For most alloys and tempers, 20 seconds at 1 A/in2 and 30 V DC at 68° [20°C] is sufficient. Stirring not needed. Rinse in warm water and dry. Use polarized light; sensitive tint helpful. |
| 4g KMnO4 1g NaOH 100mℓ water | Weck's tint etchant for Al and Al alloys, a very popular etchant for general purpose, especially good for reveal the grain of wrought alloys. Immerse sample for 15-20 seconds and gently wave the sample until the surface is colored. |
Aluminum Imaging Tips
Depending on the alloy and application the goal of analysis can differ. Some common goals of the analysis are porosity, contaminant levels, grain structure, phase percent, and dimensional measurements. Dimensional measurements can be taken and saved using one of the lower levels of our OmniMet® software. For other analysis and exporting needs more advanced versions of the OmniMet software maybe required.
Aluminum Hardness Testing Tips
| Reference Materials for Hardness Testing | ||
|---|---|---|
| ASTM | ISO | |
| Brinell | E10 | 6506 |
| Rockwell | E18 | 6508 |
| Vickers | E92,E384 | 6507 |
| Knoop | E384 | 4545 |
| Instrumented | E2546 | 14577 |
| Conversions | E140 | 18265 |
| ASM Handbook Volume 8: Mechanical Testing and Evaluation | Hardness Testing Section | |
At Buehler, the equipment offered is made to perform at least one of the following scales: Brinell, Rockwell, Vickers and Knoop. If utilizing a scale previously mentioned there are standards for the method of testing. Standards such as the ones listed in the table are good places to reference the proper method of testing for the scales. Requirements for equipment, samples, testing methods and more are described within that can help determine the correct scale.
Equipment capabilities vary in levels of automation and documentation. Some pieces are integrated with hardness testing software. Software such as Buehler’s DiaMet can assist with testing parts more efficiently, accuracy and result documentation. This can be especially helpful when a large amount of indents must be done on one part.
Related Products
All Solutions by Material
Choose a material to view Buehler's resources
Find Your Solutions
Full Lab
Metallography Solutions
Do you want to improve your process? Reach out for one-on-one help from our applications experts.
View all Products in the Buehler Product Catalog
Select a method by material
Search Buehler's Safety Data Sheets
Browse and search Buehler's product literature
