Table 1. Material specifications for ZK60A[1]

With respect to your application - the tensile strength (Ftu), tensile yield strength (Fty), elongation (e), and sometimes the compressive yield strength (Fcy) are normally called out in your customer's procurement specifications. The properties obtained reflect the location and type of test sample as well as the method of testing (again normally called out by specification).

As you undoubtedly know, magnesium is a lightweight structural material that can be strengthened by alloying and, in some cases, by heat treatment or cold work (or both). The T5 temper – cooled from an elevated temperature shaping process and artificially aged – applies to products such as castings or extrusions that are artificially aged to improve mechanical properties or dimensional stability (or both).

ZK60A is a magnesium-base alloy containing zinc and zirconium. Zirconium is an alloying addition with the ability to refine grains. This alloy has been designed to achieve its strength by artificial aging (T5) from the as-fabricated (F) temper. ZK60A has the best combination of high room-temperature strength and ductility of the wrought magnesium-base alloys, which is another reason to optimize the microstructure. It is used primarily at temperatures below 300°F (150°C). If it is not properly aged, it will be in an unstable condition, and the microstructure will be constantly changing over time.

For most applications, closed-die forgings must conform to the mechanical and physical properties of AMS 4362.

Table 2. Minimum tensile properties

AMS 4362F (revised May 2007), paragraph 3.3 (Heat Treatment) states: “Forgings shall be precipitation heat treated by heating to 300±15°F (149±8°C), holding at heat for not less than 24 hours and cooling in air. Pyrometry shall be in accordance with AMS 2750.” To comply with this specification, there is only one acceptable soak time.

Furthermore, paragraph 3.4 states: “The product shall conform to the requirements of 3.4.1, determined in accordance with ASTM B557 or ASTM B557M.” Paragraph 3.4.1.1 specifically deals with Die Forgings and states: “Shall be as shown in Table 2, determined on specimens machined from forgings 3 inches (76 mm) and under in nominal thickness at time of heat treatment with axis of specimen in area of gage length varying not more than 15 degrees from parallel to forging flow lines, on specimens machined from separately forged coupons or from forging stock representing the forgings and, in either case, heat treated with the forgings, or on specimens machined from prolongations on heat-treated forgings.”