Aluminium

Aluminium machinability

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Understanding machinability of aluminium alloys, from low strength wrought alloys to heat hardened thermally non-hardened alloys. Machinabilty of Aluminium alloys includes AlMn, AlMg1, AlMg2, AlMg3, AlMg4, AlMg5, AlMgMn and AlMg4,5Mn.

Aluminium machinability: European classification

Aluminium machinabilityFigure 1 – Definition of machinability [1]

The groups of aluminium machinability

From the point of view of machinability, aluminum alloys are divided into the following groups (in order of increasing difficulty of machining):

  • Group 1: Low strength wrought aluminium alloys;
  • Group 2.1: Deformable aluminium alloys of increased strength;
  • Group 2.2: Aluminium alloys for machining;
  • Group 3.1: Aluminium-silicon alloys with silicon content up to 10 %;
  • Group 3.2: Eutectic aluminium-silicon alloys;
  • Group 3.3: Hypereutectic aluminium-silicon alloys.

Group 1: Low-strength wrought aluminium alloys

1) Thermally non-hardenable alloys in annealed state or partially cold-worked state:

Examples of alloys:

  • AlMn,
  • AlMg1,
  • AlMgMn.

2) Heat-hardening alloys in unaged state:

Examples of alloys:

  • AlMgSi0,5,
  • AlMgSi1.

Characteristic properties for machining:

  • soft,
  • plastic,
  • low strength,
  • no solids,
  • tendency to stick to the cutting edge.

Group 2.1: High strength wrought alloys

1) Heat-hardened thermally unhardened alloys:

Examples of alloys:

  • AlMn
  • AlMg1, AlMg2, AlMg3, AlMg4, AlMg5
  • AlMgMn
  • AlMg4,5Mn

2) Heat treated alloys in aged and / or cold-worked condition:

Examples of alloys:

  • AlCuMg1
  • AlZnMg1
  • AlZnMgCu0,5
  • AlZnMgCu1,5

Characteristic properties for machining:

  • strength from 300 to 600 N / mm2 with good elongation,
  • no solids – low tool wear,
  • decrease in strength with increasing tendency to stick to the cutting edge.

Group 2.2: Aluminium alloys for machining

Thermally treated wrought alloys with additives for chipbreaking

Examples of alloys:

  • AlMgSiPb
  • AlCuBiPb
  • AlCuMgPb

Characteristic properties for machining:

  • short chips due to the presence of Pb and Bi additives;
  • strength from 280 to 380 H / mm2;
  • low tendency to stick on the cutting edge.

Group 3.1: Al-Si cast alloys with silicon content up to 10 %

1) AlSiCu alloys

Examples of alloys:

  • AlSi5Cu1
  • AlSi6Cu4
  • AlSi8Cu3

2) AlSiMg alloys

Examples of alloys:

  • AlSi7Mg
  • AlSi9Mg
  • AlSi10Mg

Characteristic properties for machining:

  • strength from 250 to 360 N / mm2;
  • increased wear of the cutting tool due to hard components of the microstructure and inclusions;
  • good chip brittleness and smooth surface;
  • the tendency to stick to the cutting edge with the content aremniya more 5 %.

Group 3.2: Low hardness Al-Si cast alloys

Al-Si alloys with a silicon content of about 12 %

Alloy example:

  • AlSi12

Characteristic properties for machining:

  • low hardness of the aluminium matrix;
  • solid metal microstructure components and inclusions;
  • high propensity to stick on the cutting edge.

Group 3.3: High hardness Al-Si cast alloys

Al-Si alloys with silicon contents exceeding 12 %

Examples of alloys:

  • AlSi18CuMgNi
  • AlSi21CuNiMg
  • AlSi25CuMgNi
  • AlSi17Cu4FeMg

Characteristic properties for machining:

  • medium strength;
  • high hardness;
  • very low plasticity;
  • high wear of the cutting tool due to very hard intermetallic particles and primary silicon;
  • high propensity to stick on the cutting edge.

Sources:

  1. Machining of Products – TALAT Lecture 3100 /P. Johne, Aluminium-Zentrale e.V., Düsseldorf – 1994
  2. Aluminum and Aluminum Allooys – ASM Speciality Handbook – Ed. J.R. Davis – 1993