How Is Aluminum Alloy Hardness Tested?

Brinell testing is the most common and generally the most suitable hardness method for aluminum and its alloys. Rockwell testing is useful when many samples require rapid results. Low-load micro-Vickers testing suits foil, strip, and very small instrument parts. Webster testing is widely used for aluminum profiles, while Leeb testing is appropriate for large castings and forgings from which samples are difficult to remove.

Brinell Hardness Testing

Select the load factor K according to alloy composition, temper, and expected hardness, where K = 0.102F/D². Then choose the indenter diameter and test force according to specimen thickness and width. Most aluminum alloys fall between 36 and 130 HBW. Only heat-treatable alloys in T4 or T6 normally exceed 130 HBW, while most commercially pure aluminum is below 35 HBW.

Rockwell Hardness Testing

Applicable scales include HRB, HRG, HRF, HRE, and HR15T. Samples above 130 HB can use HRB, HRG, or HR15T. Samples below 130 HB are better tested with HRF or HRE. Rockwell testing is not recommended below 35 HB. The minimum specimen thickness must meet the requirement for the selected Rockwell scale.

Vickers Hardness Testing for Foil and Strip

Aluminum foil and strip are thin and soft. The Chinese thickness limit for aluminum foil is 0.2 mm. Low-load Vickers or microhardness testing is therefore suitable for foil and strip less than 1 mm thick. Select the force from both material hardness and specimen thickness.

Webster Hardness Testing

Webster testing is widely used for extruded profiles, aluminum doors and windows, curtain-wall profiles, plate, and tubing. GB/T 5237-2017 specifies Webster testing for architectural profiles. The source also cites JJG 139-2001 for on-site curtain-wall profile inspection and states an acceptance value above 8 HW, corresponding to approximately 42 to 120 HBS. [TO VERIFY: Confirm the standard number and the source wording for the instrument and acceptance value.] The stated alloy range is 1xxx through 7xxx, approximately 42 to 98 HRE or 42 to 120 HBW.

Hardness Testing of Aluminum Sheet and Plate

Plate hardness helps assess hot-working performance, cold-work deformation, and heat-treatment condition. Clad and unclad sheet must be treated differently because the cladding that improves corrosion resistance can also affect the surface reading. Unclad sheet can be tested by Brinell, Rockwell, Webster, or Barcol methods; Brinell generally provides higher accuracy.

The principal Rockwell scales for aluminum sheet are HRB, HRE, HRF, and HR15T.

The conversion values are cited from HB/Z 215-1992. Webster and Barcol testers are compact portable instruments suitable for production sites, construction sites, and warehouses. For assembled components that cannot be separated, the source recommends a Barcol GYZJ 934-1 tester. A Webster range of 4 to 17 HW corresponds to approximately 42 to 120 HBS. Above 120 HBS, a Webster W-B75 or Barcol tester can be used.

No Chinese national standard is identified in the source for clad aluminum sheet. The source instead mentions Boeing BBS 7221 for 2024 and 7075 sheet and Air Canada MPS 168-13 for more detailed aluminum-sheet hardness testing.

Can Hardness Indentations Reveal Crystallographic Texture?

Improper rolling can create anisotropy, or crystallographic texture, in aluminum sheet and strip. During subsequent deep drawing, this may produce four-lobed earing. X-ray diffraction is the usual method for evaluating texture, but low-load Vickers indentations can provide a simple qualitative check when an X-ray diffractometer is unavailable.

• An annealed sample without obvious texture retains a regular square indentation with no pronounced concave or convex sides. Deep drawing produces no ears or only slight ears.
• An annealed sample with obvious texture shows inward-curving indentation sides. Ears generally form in the longitudinal and transverse directions.
• A cold-worked sample with texture shows outward-bulging indentation sides. Ears generally form at 45°.

Hardness-based monitoring is simple, inexpensive, and effective, but this indentation-shape method is qualitative rather than a substitute for full texture measurement.