Break Free from Material‑Selection Misunderstandings: Understand Aluminum Temper Designations (O, H14, H24, H32) & Hardness Selection

When purchasing aluminum coils, besides confirming alloy grades such as 1060, 3003 and 5052, buyers must specify one critical technical parameter — aluminum temper. On specification sheets, temper appears as letter‑and‑digit suffixes following alloy grades, for instance 1060‑O, 3003‑H24, 5052‑H32.

Many first‑time aluminum purchasers wonder: what is the difference between H14 and H24 for the same 3003 aluminum coil? Why do some aluminum coils crack during bending while others bend easily like soft fabric?

Simply put, aluminum temper determines hardness, tensile strength and bending ductility. Correct temper selection is a prerequisite for smooth sheet‑metal forming, deep‑drawing and bending operations. This article decodes common aluminum temper designations and their applicable scenarios.

1. Common Letter Prefixes: O‑Temper, H‑Temper and T‑Temper

Aluminum temper designations start with alphabetical characters. The major categories are shown below:
‑ O‑Temper (Annealed / Soft Temper): Fully annealed condition, representing the softest state with maximum elongation.
‑ H‑Temper (Strain‑Hardened Temper): Strength is improved via cold rolling. This is the most widely‑used temper for 1000‑series, 3000‑series and 5000‑series aluminum coils.
‑ T‑Temper (Heat‑Treatable Temper): Strength enhanced through quenching and artificial aging processes, commonly applied to 6000‑series hard alloys e.g. 6061 sheet.

2. Key Explanation: What Do Digits Following the H‑Prefix Mean?

Strain‑hardened H‑temper coils account for the vast majority of construction and manufacturing procurement. Two‑digit suffixes (example: H24) indicate fabrication sequence and hardness grade:

First digit: fabrication process combination
‑ H1x: Strain‑hardened only by cold rolling, without subsequent annealing.
‑ H2x: Cold‑rolled & strain‑hardened, followed by partial annealing (partial softening).
‑ H3x: Cold‑rolled & strain‑hardened, plus stabilizing thermal treatment (mainly for 5000‑series Al‑Mg alloys to prevent room‑temperature hardness drift)

Second digit: hardness grade (scale 1‑8; higher number equals harder material)
‑ 2: 1/4‑hard (softer, high elongation)
‑ 4: 1/2‑hard (half‑hard, the most widely‑used grade)
‑ 6: 3/4‑hard (higher strength, stiffer)
‑ 8: Full‑hard (extremely hard, very low elongation)

Practical example:
3003‑H14 and 3003‑H24 deliver roughly equivalent strength and hardness (both 1/2‑hard). The difference lies in H24 receiving post‑cold‑rolling partial annealing, which lowers internal stress. H24 is less prone to micro‑cracks under sharp bending or roll forming and delivers more stable paint‑film adhesion.

3. Reference Table for Common Aluminum Tempers & Application Scenarios

4. How to Select Temper According to Your Fabrication Process

Select temper before placing orders based on your factory processing equipment:

1. If tight 90° or even 180° lock‑seam bending / roll‑forming is required:
 ➔ Prioritize H24 or H14 (1/2‑hard). Sufficient stiffness maintains profile shape without corner cracking.

2. If deep‑drawing or heavy stamping operations are required:
 ➔ Prioritize O‑temper or H22.

3. For 5000‑series (e.g.5052) aluminum coils used outdoors or requiring bending:
 ➔ Select H32 for most stable material performance.

4. For large flat panels demanding high flatness and strength with no bending required:
 ➔ Higher‑hardness grades such as H18 or H38 are acceptable.