Aluminum Alloy Comparison: 6061 vs 7075 vs 5052

Not all aluminum is the same. Different alloys offer different combinations of strength, machinability, weldability, and corrosion resistance. This guide compares the most common aluminum alloys for machining and fabrication.

Understanding Aluminum Designation

The 4-digit numbering system:

• 1xxx: Pure aluminum (99%+), soft, excellent corrosion resistance
• 2xxx: Copper alloy, high strength, poor weldability
• 3xxx: Manganese alloy, moderate strength, good formability
• 5xxx: Magnesium alloy, good strength, excellent weldability
• 6xxx: Mg-Si alloy, versatile, good weldability and strength
• 7xxx: Zinc alloy, highest strength, limited weldability

Temper designations (T6, T651, etc.) indicate heat treatment condition.

Common Alloys Compared

6061-T6: The Workhorse

The most common structural aluminum alloy:

• Strength: Good (45 ksi tensile)
• Machinability: Excellent, great surface finish
• Weldability: Good with 4043 or 5356 filler
• Applications: Structural frames, brackets, fixtures, general machining
• Note: Heat treatment affected by welding—HAZ loses strength

7075-T6: Maximum Strength

Aircraft-grade, highest strength aluminum:

• Strength: Excellent (83 ksi tensile—comparable to mild steel)
• Machinability: Good, but harder on tooling
• Weldability: Poor—prone to cracking, rarely welded
• Applications: Aircraft structures, high-stress parts, gears, shafts
• Note: Susceptible to stress corrosion; typically joined mechanically

5052-H32: Weldability Champion

Best choice when welding is the primary concern:

• Strength: Moderate (33 ksi tensile)
• Machinability: Fair (soft, can gum up tools)
• Weldability: Excellent, maintains properties in HAZ
• Applications: Tanks, marine hardware, sheet metal fabrication
• Note: Cannot be heat treated; work-hardened only

Other Notable Alloys

2024-T3

High strength, good fatigue resistance, but poor corrosion and weldability. Classic aircraft skin material, often Alclad for corrosion protection.

6063-T6

Architectural alloy—excellent surface finish and anodizing response. Slightly lower strength than 6061. Used for extrusions, window frames, trim.

MIC-6 (Cast Tooling Plate)

Cast aluminum with excellent flatness and stability. Ideal for fixture plates, vacuum tables, and tooling. Machines well, holds tolerances.

Selection Guidelines

Choose 6061 When:

• You need a balance of properties
• Welding is required but strength matters
• Cost is a factor
• This is your default choice

Choose 7075 When:

• Maximum strength is critical
• No welding is required
• Weight savings justify the cost premium
• Fatigue performance matters

Choose 5052 When:

• Welded construction is primary
• Marine or corrosive environment
• Sheet metal forming required
• Lower strength is acceptable

Machining Considerations

• All aluminum: Use high RPM, sharp tools, appropriate chip load
• Soft alloys (5052, 1100): Can gum up; use coated tools, cutting fluid
• Hard alloys (7075, 2024): Better chip breaking, watch for work hardening
• Finish: 6061 and 6063 anodize beautifully; 7075 less so

Material selection is a trade-off between properties, cost, and manufacturability. When in doubt, 6061-T6 handles most situations. Upgrade to 7075 for strength or 5052 for weldability as specific requirements demand.