What is the best aluminium for CNC machining?

1、Answer

 

• 7075-T6 (highest strength, tensile strength ≥572MPa): Used in aerospace and high-load scenarios but harder to machine (requires carbide tools);
• 5052-H32 (best corrosion resistance): Suitable for marine/chemical equipment but with lower strength (tensile strength ≤262MPa).

2、Expansion

Core Grade Characteristics and Selection Logic

1. 6061-T6: The “Versatile Choice” for CNC Machining
   • Composition & Properties: Contains 1% silicon + 0.8% magnesium, strengthened via T6 heat treatment (solution annealing + artificial aging) while maintaining good ductility (elongation ≥12%).
   • Machining Advantages:
     • Low cutting resistance (30% less than 7075), compatible with high-speed steel (HSS) tools, feed rate up to 800mm/min;
     • Low thermal expansion coefficient (23.6×10⁻⁶/℃), ideal for precision machining (tolerance ±0.02mm).
   • Typical Applications:
     • Mechanical parts (fixtures, gearboxes), drone frames (lightweight + vibration resistance), industrial radiators (thermal conductivity 180W/m·K).
2. 7075-T6: The “Performance King” for High-Strength Scenarios
   • Composition & Properties: Contains 5.6% zinc + 2.5% magnesium, strength approaching steel (hardness HB≥150) but with poor corrosion resistance (requires plating protection).
   • Machining Challenges:
     • Prone to tool adhesion (needs diamond-coated or carbide tools, cutting speed ≤300mm/min);
     • High residual stress (stress-relief annealing required after rough machining, adding 20% cost).
   • Typical Applications:
     • Aerospace structures (wing ribs, landing gear), racing components (30% weight reduction with 50% load increase), high-pressure valves (pressure resistance ≥20MPa).
3. 5052-H32: The “Specialized Choice” for Corrosion Resistance
   • Composition & Properties: Contains 2.5% magnesium (copper-free), strengthened via cold working (H32 = 1/4 hardening), salt spray corrosion resistance 5x that of 6061.
   • Machining Limitations:
     • Prone to built-up edge (feed rate must be reduced below 0.1mm/r);
     • Unsuitable for high temperatures (service temperature ≤65℃).
   • Typical Applications:
     • Marine engineering parts (ship fittings, seawater pipelines), chemical equipment casings (acid/alkali resistance), laptop casings (smooth anodized surface).

Machining Parameters and Cost Optimization

• Tool Selection:
  • 6061 can use standard HSS end mills ($20–$50 per tool);
  • 7075 requires tungsten carbide (WC) or PCD tools ($200–$800 per tool), with 5–10x longer lifespan.
• Coolant Strategies:
  • Water-soluble coolant for 6061 (prioritizes cooling);
  • Oil-based coolant for 7075 (prioritizes lubrication to prevent tool bonding).
• Cost Comparison (for 100 aluminum blocks)：

  Grade	Material Cost/Unit	Machining Time/Unit	Total Time	Total Cost
  6061-T6	$15	30 minutes	50 hours	$850
  7075-T6	$25	1 hour	100 hours	$1,750
  5052-H32	$20	45 minutes	75 hours	$1,275

Special Scenario Extensions

• High Surface Finish Requirements: 6063-T5 (0.35% silicon) is preferable, achieving surface roughness Ra0.8μm without secondary polishing (e.g., optical instrument casings).
• Extreme Lightweight Needs: 2024-T3 (4.4% copper) offers strength comparable to 7075 but with 3% lower density (2.78g/cm³), used for aerospace weight-sensitive parts (satellite brackets), though prone to discoloration after anodizing.
• Rapid Prototyping: Pre-machined 6061-T6 billets (e.g., Φ100mm aluminum rods) are readily available, saving 3 days of lead time compared to custom 7075 billets.