What distinguishes the mechanical properties of 8011-O versus H18 temper?
The 8011-O (annealed) temper exhibits the lowest hardness with typical tensile strength around 80-100 MPa, making it ideal for deep drawing applications. In contrast, H18 temper achieves the highest hardness through 75% cold work, reaching tensile strengths of 130-150 MPa. The elongation difference is dramatic - O temper allows 20-25% elongation while H18 drops to 3-5%. The H18 temper's yield strength approaches 120 MPa compared to O temper's 30-40 MPa. These properties make O temper suitable for complex forming while H18 serves best for rigid packaging applications.
How does the H22 temper balance formability and strength in 8011 alloy?
H22 represents a partially strain-hardened condition with tensile strength between 100-120 MPa, offering a middle ground between O and H18 tempers. It retains 12-15% elongation, allowing moderate forming operations like bending or shallow drawing. The temper achieves this balance through approximately 25% cold reduction after annealing. Compared to H12 (10-15% cold work), H22 provides better springback control for formed parts. This makes H22 popular for pharmaceutical foil lids requiring both stiffness and seal integrity.
What surface characteristics differ among these tempers?
The O temper displays the roughest surface (Ra 0.4-0.8μm) due to recrystallization during annealing. H12-H18 tempers progressively develop smoother surfaces (Ra 0.2-0.4μm) as cold rolling refines the microstructure. H22 temper shows directional "mill finish" patterns from intermediate rolling passes. All tempers maintain the alloy's natural aluminum oxide layer, though H18 may require additional cleaning to remove rolling lubricants. Surface brightness typically increases with higher H-numbers due to work hardening effects.
Why would manufacturers choose 8011-H14 for food packaging?
H14 temper (25-30% cold work) provides optimal combination of 110-125 MPa tensile strength and 8-10% elongation for lid stock applications. It demonstrates better puncture resistance than H12 while maintaining sufficient formability for sealing processes. The temper resists edge cracking during blanking operations better than H16/H18. Its moderate hardness (60-70 HB) prevents excessive tool wear during high-speed converting. Additionally, H14 shows excellent foil rolling quality with consistent 6-50μm thickness tolerances.
How do thermal properties vary across these tempers?
All tempers maintain the base alloy's thermal conductivity (~220 W/m·K) as cold working minimally affects this property. However, recrystallization temperature differs significantly - O temper begins at 300°C while H18 requires 350°C+ due to stored energy from cold work. The H22 temper shows intermediate thermal stability up to 320°C. Electrical conductivity remains stable at 59-61% IACS across all tempers. Annealing studies show H-tempers progressively revert toward O-state properties when heated above 200°C for extended periods.
