A Modified Cast-on Method for the Reinforcement of Aluminum Castings with Dissimilar Metals
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LIGHTWEIGHT metals and alloys such as aluminum and magnesium have found increased applications in replacing iron and steels in the defense and automotive industries for weight reduction of vehicles. Such substitutions, however, have often resulted in compromised performance and/or reliability. A wellknown solution to some of the performance and reliability problems associated with the use of light weight casting materials as a substitute for cast irons and steels has been to provide high strength inserts at critical locations where severe wear or high stress is known to occur. Critical locations are defined as areas in a casting where the stresses or temperatures exceed the capabilities of the lightweight materials. Inserts of expensive material can also be used at critical areas where severe corrosion is known to occur so that inexpensive material can be used for making the rest of a component/casting. The concept of joining dissimilar materials into a single component to take best advantage of the unique properties of each material is not new.[1–3] Over the years, it has been referred to as bimetal or bimetallic construction, composite design, duplex materials, and others.[4–6] Cast-on method is one of the most cost-effective methods for bonding iron or steel to lightweight materials using a metal casting process.[1–3] Al-Fin is one of such methods which involves dip coating the steel insert in molten metal with low melting temperatures,
QINGYOU HAN, formerly with Oak Ridge National Labs, Oak Ridge TN, is now Professor with Purdue University, 401 N. Grant Street, West Lafayette, IN 47906. Contact e-mail: [email protected] Manuscript submitted December 5, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
such as zinc or aluminum alloys, and casting-in the coated steel into aluminum castings. The method has found some applications but has not found general acceptance in applications of high performance, reliability, and durability requirements. One explanation for this is the difficulty of achieving an effective, durable metallurgical bond between the insert and the adjacent lightweight cast material. Beile and Lund[6] disclose a bonding technique for achieving metallurgical bonding requiring an absolutely clean surface on the inserts. Practical methods to prevent oxidation are to employ vacuum, insert atmospheres, or reducing atmospheres. It has been reported that the production of an intimate bond may be prevented by the presence of an oxide film on the outer surface of the aluminized coating on the insert.[7] A few approaches have been undertaken in an attempt to achieve an acceptable metallurgical bond between inserts and cast metals.[7,8] These approaches utilize pre-coatings to protect the insert surface from oxidation and other contaminations. However, none of these methods has been entirely successful in producing consistent, high strength bonds between inserts and lightweight casting material that will meet the long-term demands for reliability required in certain applications such as the manufacture of
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