The discovery of γ′ hardening early in the 20th century seeded a continuous evolution of a remarkable family of alloys, known as the superalloys. The sequence of their development will be traced in this article. The theories of alloying and hardening mechanisms will be discussed as each played an essential role in the progressive development of the superalloys, as did a number of processing discoveries that are reviewed here.

A new procedure for blending die-cast Mg-Al alloys by semisolid processing to achieve controlled variations in microstructure and properties has been investigated. Granules of AM60B and AZ91D have been blended in varying proportions and Thixomolded at nominal solid fractions of 0.1 and 0.3, respectively. As-molded microstructures and the role of interdiffusion during processing have been analyzed in detail by scanning electron microscopy, transmission electron microscopy, and electron microprobe analysis. Tensile properties and failure modes have been analyzed and a strength model that considers solid solution strengthening of Al in the unmelted particles and a rule-of-mixtures behavior for microstructural components is proposed.

No abstract

No abstract

The technical and commercial development of Thixomolding® of magnesium (Mg) alloys is described. Based on the MIT semi-solid casting discovery, Dow Chemical adaption to Mg and Thixomat technical findings, Thixomat commercialized this process world-wide with Japan Steel Works (JSW) and numerous licensees in 13 countries. Some 480 Thixomolding machines have been commissioned by JSW to produce a wide range of parts for application in the communication/electronic, auto, sporting goods and hand-held tool markets. The advantages over conventional casting of Mg have been established in cleanliness, safety, worker comfort, machine portability, longer die life and reduced scrap. The competiveness of Thixomolding Mg has been enhanced by more durable and less expensive machine parts, longer die life, higher raw material yields by using hot nozzles and amenability to using recycled Mg scrap. The portability of this “foundry inside a machine” and availability of pre-owned machines allows quick set-up of Thixomolding operations. Several technical advances in Thixomolding are described. Solids content was optimized. Hot nozzles increased the part yield to >90% of the granule Mg alloy feed. Special steel barrels and liners are available to substitute for expensive Superalloys. In addition to conventional AZ91D and AM60, a wide range of Mg alloys can be Thixomolded. With Dead Sea Magnesium, AM70-TH and AJX810-TH were developed for improved ductility or creep strength. Low porosity and fine grain size of Thixomolding open the door to blister-free thermomechanical processing (TTMP) to boost the tensile and fatigue strength and ductility.