We continue our discussion of aluminum and aluminum alloys by focusing on the individual alloys series. Let’s talk about cast alloys, whichcan be classified as follows.

The first digit indicates the alloy group according to the major alloying element. These include:

• 1xx.x aluminum, 99.0% minimum
• 2xx.x copper (4-4.6%)
• 3xx.x silicon (5-17%) with added copper and/or magnesium
• 4xx.x silicon (5-12%)
• 5xx.x magnesium (4-10%)
• 7xx.x zinc (6.2-7.5%)
• 8xx.x tin
• 9xx.x other alloying elements

The second two digits identify aluminum alloy or indicate the alloy purity.

In the alloys of the 1xx.x series, the second two digits indicate the level of purity of the alloy. For example (in percentages), 150.0 means a minimum of 99.50% aluminum in the alloy and 120.1 means a minimum of 99.20% of aluminum in the alloy.

In all other groups of cast aluminum alloys (2xx.x through 9xx.x), the second two digits signify different alloys in the group. The digit after the decimal point indicates the product form, with casting designated by “0” and ingot designated by “1” or “2” (depending on chemical composition limits).

A modification of the original alloy or higher impurity limits are indicated by a serial letter before the numerical designation. The serial letters are assigned in alphabetical order starting with A (omitting I, O, Q and X). The letter “X” is reserved for experimental alloys).

Characteristics

Aluminum-copper cast alloys (2xx.x series)

• Heat-treatable
• High strength
• Low corrosion resistance (susceptible to stress-corrosion cracking)
• Low fluidity
• Low ductility
• Susceptible to hot cracks

Aluminum-silicon-copper/magnesium cast alloys (3xx.x series)

• Heat-treatable
• High strength
• Low ductility
• Good wear resistance
• Decreased corrosion resistance (in copper-containing alloys)
• Good fluidity
• Good machinability (in copper-containing alloys)

Aluminum-silicon cast alloys (4xx.x series)

• Non-heat-treatable
• Moderate strength
• Moderate ductility
• Good wear resistance
• Very good cast properties
• Good corrosion resistance

Aluminum- magnesium cast alloys (5xx.x series)

• Non-heat-treatable
• High corrosion resistance
• Good machinability
• Good appearance when anodized
• Moderate cast properties

Aluminum-zinc cast alloys (7xx.x series)

• Heat-treatable
• Good dimensional stability
• Good corrosion resistance
• Poor cast properties
• Good machinability (in copper-containing alloys)

Aluminum-tin cast alloys (8xx.x series)

• Non-heat-treatable
• Low strength
• Very good wear resistance
• Good machinability

References