Aluminum alloys

Next to steel, aluminum is the most commonly used and commercially available metal. Its light weight and high strength-to-weight ratio make it a good choice for just about anything you can make out of metal. Its alloys generally that have excellent corrosion resistance, good workability (machinability) and good to excellent weldability, are often used in marine applications (marine grade aluminum).

The Aluminum Association, Inc. uses a standard four-digit numerical system to indicate the main alloying additives, as shown below:

  • 1xxx - Pure aluminum at least 99.0%, no alloying elements
  • 2xxx - Main alloying element copper (Cu)
  • 3xxx - Main alloying element manganese (Mn)
  • 4xxx - Main alloying element silicon (Si)
  • 5xxx - Main alloying element magnesium (Mg) (marine grade alloys)
  • 6xxx - Main alloying elements magnesium (Mg) and silicon (Si) (marine grade alloys)
  • 7xxx - Main alloying element zinc (Zn)
  • 8xxx - Other elements
  • 9xxx - Not used

In addition, a temper designation is used to show the cold-working and heat-treating histories:

  • F - fabricated
  • H - strain hardened
  • O - annealed (brought to desired consistency, texture or hardness by a process
          of gradual heating and cooling)
  • W - solution heat-treated
  • T - Heat treated to produce stable tempers other than F, O, H or W

The following table gives main features of some marine grade aluminum alloys (series 5xxx and 6xxx; in blue font) and a few others for reference:

Aluminum Grade-Temper General Yield strength
(psi)
Ultimate Tensile
Strength (psi)
Workability Weldability Hardness
(Brinell)
  Chemistry   
Pure Al
1xxx Series
Low strength (soft), non-magnetic, highly electrically and thermally conductive, high corrosion resistance. Used for wrought aluminum elements. 24,000 29,700     12-55 Al 99.0% min
2011-T3 Most workable of all aluminum alloys, excellent surface finish 43,000 55,000 Excellent Average 95 Al 91.2-94.6%
Bi 0.2-0.6%
Cu 5.0-6.0%
Fe 0.7% max
Mg 2.1-2.9%
Pb 0.2-0.6%
Si 0.4% max
2024-T3 Very strong compared to most aluminum alloys. High percentage of copper makes it susceptible to corrosion. High fatigue resistance. Used mainly in aerospace applications. 50,000 70,000 Average Non-weldable 120 Al 95.7-97.7%
Cr 0.1% max
Cu 3.8-4.9%
Fe 0.5% max
Mg 1.2-1.8%
Mn 0.3-0.9%
Si 0.5% max
5052-H32 Marine grade. Most suited for forming operations, very good corrosion resistance. 28,000 33,000
12% elong.
Fair Good 60 Al 95.7-97.7%
Cr 0.15-0.35%
Cu 0.1% max
Fe 0.4% max
Mg 2.2-2.8%
Mn 0.1% max
Si 0.25% max
5083-H321 Marine grade. The highest strength non-heat-treatable aluminum alloy in commercial use. It retains excellent tensile strength in the weld zone. Excellent corrosion resistance.
(Platypus is built in this alloy)
33,000 46,000
16% elong.
Good Excellent 85 Al 92.4-95.6%
Cr 0.05-0.25%
Cu 0.1% max
Fe 0.4% max
Mg 4.0-4.9%
Mn 0.3-1.0%
Si 0.4% max
Ti 0.15 max
5086-H32 Marine grade. Medium to high strength non-heat-treatable alloy. More formable than 5083. Excellent corrosion resistance. Most often used to build boat hulls (in addition to 5052 or 6061) due to stress corrosion cracking resistance. 30,000 42,000
12% elong.
Excellent Good 78 Al 93-96.3%
Cr 0.05-0.25%
Cu 0.1% max
Fe 0.5% max
Mg 3.5-4.5%
Mn 0.2-0.7%
Si 0.4% max
Ti 0.15% max
6061-T6 Marine grade, often used to build boat hulls and other components. The most often used aluminum alloy for its strength, heath treatability, workability and weldability. 40,000 45,000
17% elong.
Good Good 95 Al 95.8-98.6%
Cr 0.04-0.35%
Cu 0.15-0.40%
Fe 0.70%
Mg 0.8-1.2%
Mn 0.15% max
Si 0.4-0.8%
Zn 0.25%
6063-T52 Softer and lower strength than 6061, good for forming, high surface finish, excellent for anodizing. 21,000 27,000 Good Good 60 Al 97.5% max
Cr 0.1% max
Cu 0.1% max
Fe 0.35% max
Mg 0.45-0.90%
Mn 0.1% max
Si 0.2-0.6%
6262-T6511 Used when significant machining is required, it contains lead and bismuth to partially lubricate the cutting tool. Good strength and corrosion resistance. High surface finish possible. 27,600 31,900 Excellent Good 71 Al 94.6-97.8%
Bi 04-0.7%
Cr 0.04-0.14%
Cu 0.15-0.40%
Fe 0.7% max
Mg 0.8-1.2%
Mn 0.15% max
Pb 0.4-0.7%
Si 0.4-0.8%
7075-T6 One of the highest strength aluminum alloys, in T6 temper higher than most mild steels. Good machinability, good corrosion resistance, good for anodizing. Used in aircraft industry. 73,000 83,000 Good Non-weldable 150 Al 87.1-91.4%
Cr 0.18-0.28%
Cu 1.2-2.0%
Fe 0.5% max
Mg 2.1-2.9%
Mn 0.3% max
Zn 5.1-6.1%

Note: The above details are listed for an approximate orientation only. They have been collected from various sources and have not been verified.

  1. The Yield Strength specifies the force at which the material it acts on yields beyond its elasticity range and deforms permanently (dents or bends).
  2. The Ultimate Tensile Strength gives the force that breaks the material. For the marine grade aluminum in the above table, this figure is further accompanied with the percentage of elongation of the material sample, a stick of 1/2 inch (12.7 mm) diameter, at the moment of breakage. That elongation is proportional to the dent the same force would exert on a sheet plate of the same material.
  3. psi (pound-per-square-inch, or more correctly pound-force-per-square-inch) = lbf/in2
  4. 1 ksi = 1,000 psi = 6.89476 MPa (mega-Pascals), if you wish to recalculate above ultimate tensile and yield strengths.
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