Casting answers & advice.

Q Casting blueprints we receive from our customers often specify aluminum alloy 356.1 or 356.2. Are these casting of ingot specifications? Can I ship castings against these specs?

Background: The specification of a particular aluminum alloy for a cast component is typically based upon the mechanical properties and end use requirements. The chemistry of the alloying elements and impurities is designated in the aluminum alloy specification. The system used to designate aluminum casting alloys in the U.S. was first adopted in 1954 and is monitored by the Aluminum Association (AA). Commonly known as the AA 'Pink Sheets,' the system designates individual aluminum metalcasting alloys using a three-digit number plus a decimal (Table 1).

The system denotes the chemical composition limits of aluminum alloys and specifies the percentage of each alloying element, of an allowable chemistry range. The system categorizes the alloys by groups (or series) according to their major alloying elements.

The balance of the three-digit number identifies the various individual alloys within each alloy series. Some alloy designations include a letter before the three-digit alloy designation, which distinguishes between alloys that fall within the alloy chemistry ranges, but differ slightly in percentages of alloying elements or impurities.

The 'Pink Sheet' designations apply to aluminum alloys in the form of both castings and ingot, and the single digit following the decimal indicates the form of the product being specified:

* XXX.0--casting;

* XXX.1--ingot used to make the casting;

* XXX.2--ingot used to make the casting (having typically Lighter chemical limits than the XXX.1 ingot designation).

The 'Pink Sheets' also list the 'product' of form of each alloy. The XXX.1 and XXX.2 alloys are listed as ingot and the XXX.0 are listed by the casting process typically used to make products from the alloy--D for diecast, S for sand castor P for permanent mold.

The XXX.1 ingot version is often supplied as secondary product that has been produced from recycled scrap metal, and the XXX.2 ingot is generally produced us primary aluminum directly from ore by the reduction cell process.

Recommendation: When 356.1 or 356.2 is listed as the alloy specification on casting blueprints, it should designate the chemistry of the ingot used to make castings, not the final castings. The casting specification (XXX.0) includes chemistry that is typically somewhat different than the ingot specification of the same number to allow for slight chemistry changes that can occur during the remelting process. The addition of casting returns such as gates, risers and scrap castings to the charge material also can modify the casting chemistry.

The primary difference is that the XXX.0 casting chemistry specifications allow for some magnesium loss and iron of zinc pick up that may be experienced during processing. The alloy chemistry of the final 356 cast component should fall with the limits of the 356.0 specification, but may not meet the chemical specification for the 356.1 ingot.

If the casting blueprint designates 356.1 as the casting alloy, it is still improper to designate the final castings as 356.1. Technically, components from 356.1 ingot should be shipped designated as 356.0 castings--even if they meet the XXX.1 specifications. There could be problems if a metalcasting facility accepts an order that designates 356.1 or XXX.2 alloy for the castings.

For example, mechanical properties listed for heat treat tempers typically refer to XXX.0 properties, such as 356.0-T6. Since there are no temper properties for ingot alloys (there are no listed properties for 356.1-T6), the final castings may not technically conform to the requirements. This proper designation of XXX.1 or XXX.2 to refer to ingot and XXX.0 for casting is a 'fine-print' distinction with which many casting designers and purchasers may not be familiar.

Table 1. Segment of the Aluminum Association 'Pink Sheet.'

AA #     Product     Si         Fe        Cu     Mn       Mg

356.0      S&P     6.5-7.5      0.6      0.25   0.35   0.20-0.45
356.1     Ingot    6.5-7.5     0.50      0.25   0.35   0.25-0.45
356.2     Ingot    6.5-7.5   0.13-0.25   0.10   0.05   0.30-0.45
A356.0     S&P     6.5-7.5     0.20      0.20   0.10   0.25-0.45
A356.1    Ingot    6.5-7.5     0.15      0.20   0.10   0.30-0.45
A356.2    Ingot    6.5-7.5     0.12      0.10   0.05   0.30-0.45
B356.0     S&P     6.5-7.b     0.09      0.05   0.05   0.25-0.45
B356.2    Ingot    6.5-7.5     0.06      0.03   0.03   0.30-0.45
C356.0     S&P     6.5-7.5     0.07      0.05   0.05   0.25-0.45
C356.2    Ingot    6.5-7.5     0.04      0.03   0.03   0.30-0.45
F356.0     S&P     6.5-7.5     0.20      0.20   0.10   0.17-0.25
F356.2    Ingot    6.5-7.5     0.12      0.10   0.05   0.17-0.25

                                         Others

AA #     Product    Zn       Ti       Each   Total   Aluminum

356.0      S&P     0.35     0.25      0.05    0.15   remainder
356.1     Ingot    0.35     0.25      0.05    0.15   remainder
356.2     Ingot    0.05     0.20      0.05    0.15   remainder
A356.0     S&P     0.10     0.20      0.05    0.10   remainder
A356.1    Ingot    0.10     0.20      0.05    0.15   remainder
A356.2    Ingot    0.05     0.20      0.05    0.15   remainder
B356.0     S&P     0.05   0.04-0.20   0.05    0.15   remainder
B356.2    Ingot    0.03   0.04-0.20   0.03    0.10   remainder
C356.0     S&P     0.05   0.04-0.20   0.05    0.15   remainder
C356.2    Ingot    0.03   0.04-0.20   0.03    0.10   remainder
F356.0     S&P     0.10   0.04-0.20   0.05    0.15   remainder
F356.2    Ingot    0.05   0.04-0.20   0.05    0.15   remainder

The above chart shows chemical composition limits for 356 aluminum
alloys. Alloys designated with a XXX.0 refer to chemistry for a
casting, while alloys designated with a XXX.1 or XXX.2 refer to
ingot chemistries.

The information in this column was supplied by the AFS Aluminum Division.

Recommendations are the opinion of the AFS Technical Dept. based on referenced literature and experienced. If you need assistance with a technical issue, fax or email your question to: Casting Answers & Advice, c/o MODERN CASTING, at 847/824-7848 or [e-mail]