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MDL’s Aluminum Casting Material Offerings and the Rational for Choices for Microwave Castings for RF Applications.

By John Kane, Design and Manufacturing Engineer, @MDLlab

MDL has been producing Microwave Waveguide Castings for well over 50 years. During that time, one could say we “know a thing or two” about the fabrication process of Castings and what materials are best suited and mostly used in the Waveguide RF Industry.                                                                                                                                                                
MDL offers two choices of Aluminum materials D712 and A356.

The Aluminum materials can be separated into two categories;
a.) Aluminum that can be Brazed with other Aluminum Alloys (D712 material).
b.) Aluminum that cannot be Brazed with other Aluminum Alloys (A356 material).

The descriptions below provide just some of the beneficial characteristics of each of the Aluminum materials MDL offers.                                                                                                                     
  

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Alloy 712 is employed when a combination of good mechanical properties without heat treatment is needed. It also shows good shock, corrosion resistance, machinability and dimensional stability. No distortion is exhibited when D712 is heated. After brazing, the D712 alloy will regain its original strength by natural aging. (** D712 will age harden to T6 Temper over time.**)                                                                                                                                   
Ability to Cast —Alloy D712 has fair to good cast-ability. Although its pressure tightness and resistance to hot cracking are only fair, the alloy’s fluidity and solidification shrinkage tendency are rated as good.
Machinability—the machining characteristics of the D712 alloy are excellent. Fast speeds and feeds and wear-resistant tools correctly ground for cutting aluminum are recommended.
Finishing—Polished finishes are good. The anodized finish is good, and the color is medium golden yellow. Ability to Weld —Welding characteristics are fair for most common methods. The D712 alloy is NECESSARY for brazing.
Corrosion Resistance—the D712 alloy has good natural resistance to corrosion, and good additional protection is received from chemical conversion coatings.                                                  

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 Alloy A356 has greater elongation, higher strength and considerably higher ductility than D712. It has these improved mechanical properties because impurities are lower in A356 than in D712. Typical applications are airframe castings, machine parts, truck chassis parts, aircraft and missile components, and structural parts requiring high strength.

 Ability to Cast—all casting characteristics are excellent for this alloy.
Machinability—Alloy A356 has good machinability. Abrasiveness can be overcome and high tool wear can be minimized by using sharp, carbide-tipped tools with high rakes and clearances. Moderate to fast speeds are recommended.
Finishing—Electroplated finishes are good. Chemical conversion coatings give good protection, but anodized appearance is only fair. Mechanical finishes on A356 are good.
Ability to Weld—all common welding methods are excellent for joining this alloy. Brazing is not performed for this Alloy.
Corrosion Resistance—the A356 alloy has good resistance to most forms of corrosion.The following Tables list the compositions and the typical properties of the D712, A356 and A380 Aluminum Alloys. A380 is the most common and most cost effective Aluminum Alloy used in Die Casting.

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Pictures of Aluminum Die Cast parts courtesy of Viking SATCOM.

When choosing Casting for your Microwave Waveguide system, please consult MDL on your Casting material choice. MDL’s 50+ years of experience will guide you to the appropriate choice. Future considerations should include your rate of production. D712 and A356 Castings are typically produced in low to moderate volumes. Castings produced with Die’s should only be considered in High Volume production rates (due to the expense of the Die).

Visit our website at www.mdllab.com or call 1-781-292-6684 for your casting needs.