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Semi-solid processing (SSM) has many advantages in that the alloy is cast at lower temperatures (i.e., in the two-phase region) giving rise to reduced die wear, as well as giving rise to novel microstructures. The resultant SSM processed castings are dendrite-free and do not contain hot tears; rather, the SSM structure is globular, and the liquid phase surrounding the globules acts as a “lubricant” during processing. Moreover, the flow of the slurry into the die cavity is more laminar than turbulent, since the starting metal is in the mushy region. This concept of SSM processing was realized by the development of a continuous process titled: CRP - Continuous Rheo-conversion Process. In this process, one allows the incipient solidification of alloy melt(s) under the combined effects of forced convection and rapid cooling rates. In the CRP, two liquids held at particular level of superheat, are passively mixed within a reactor.

Squeeze casting is considered a “high integrity” casting process because it imparts qualities (higher tensile properties, in particular ductility due to reduced or absence of porosity in the matrix, and the ability to heat treat) to a metal that are difficult to achieve with conventional casting techniques including gravity permanent mold (GPM) and high pressure, high velocity (HPDC) die casting. In recent years, the squeeze casting process has been widely used with various aluminum alloys to manufacture near-net shape automotive components requiring high strength, ductility or pressure tightness. However, with the emphasis on weight reduction, lower cost and improved performance of structural components, alternative lightweight materials including magnesium are now being seriously considered. Unfortunately, the use of magnesium as a structural material has been hindered by the lack of data on mechanical properties and the lack of new improved casting methods.

The basic data on the mechanical properties of a casting are frequently obtained from a tensile test, in which a suitable specimen machined from the casting is subjected to increasing axial load until it fractures. The engineering tension test is widely used by casting manufacturers as an acceptance test for customer specifications. However, tensile bars machined from castings often provide undesirable information, thereby leading one to question the part integrity. This paper, therefore, discusses the various factors that affect tensile properties obtained from specimens machined from actual castings.

Semi-solid metal (SSM) casting of aluminum components is currently establishing itself as a viable process for critical applications in the automotive industry. SSM casting processes compete favorably on both cost and performance with other casting techniques including gravity permanent mold (GPM), conventional high pressure die casting (HPDC) and squeeze casting. In this paper the various SSM casting routes in use today are reviewed. The two categories of SSM processes are thixocasting (involves the use of electro-magnetically stirred or grain-refined billets) and rheocasting (slurry produced directly from the liquid phase). The former requires a billet that needs to be reheated and processed, whereas the latter is cast directly from the liquid state. Also described here are new approaches to slurry making. These include the Slurry on Demand (SoD) process from AEMP, the Sub Liquidus Casting (SLCR) process from THT, and Diffusion Solidification.

This paper provides a description of commercially available die casting processes including conventional die casting process (high pressure, high velocity), squeeze casting (high pressure, controlled cavity fill rate), semi-solid metal casting, and Vacural™ (a variation of the conventional die casting process). The various automotive products made using these processes are also reported in the study. In this study, the mechanical (tensile, impact, fatigue strength and fracture toughness) and wear properties are compared among the above processes. Results indicate that mechanical and wear properties of aluminum alloys made using the “high integrity” casting processes (squeeze, semi-solid metal casting and Vacural™) are superior to those of conventional die castings.

The emergence of squeeze casting process for aluminum alloys has given material and design engineers a new alternative to conventional casting techniques: gravity permanent mold (GPM) and conventional (high velocity, high pressure) die casting. In recent years, the squeeze casting process has been applied to near net shape products requiring high impact strength, high fatigue strength, pressure tightness, or high wear resistance. This paper provides both a description of the HVSC squeeze casting process and examples of select components manufactured at CONTECH. In this study, the mechanical (tensile, impact, fracture toughness, fatigue strength) and wear properties of various aluminum alloy squeeze castings are also compared with those of gravity permanent mold and conventional die-castings. Results indicate that mechanical and wear properties of aluminum squeeze castings are superior to those of gravity permanent mold and conventional die-castings.

A pilot production program was initiated to evaluate the suitability of recycled AZ91D magnesium alloy ingot in a production steering column component. Class I A291D magnesium alloy scrap was remelted and refined using an argon flotation technique. The non-metallic inclusion content of the metal was continually monitored by a newly developed light reflectance technique. In addition, chemistry was checked and adjusted to bring the metal into ASTM chemistry specifications. Analysis of the refining operation with respect to cleanliness showed that modifications to the argon gas distribution were necessary. After the necessary modifications were implemented, metal refining efficiency increased. The refined alloy was cast into 11 kg (25 lb.) ingots that were subsequently remelted at Contech's production facility. Parts were produced under the same conditions used for “virgin” metal, and the metal quality was again assessed with the light reflectance technique.

Increased requirements for crash energy management in automotive interiors have led to increased application of magnesium alloy AM50A. Successful integration of this new alloy with hot chamber diecasting process technology requires substantial adjustment and attention to processes and practices. This paper details the conversion of magnesium AZ91D steering column diecastings to high ductility structural alloy. Description is given of the changes made to foundry practices, casting parameters, process compliance monitoring, and hot end component management. The resulting improvements allow production of components comparable to the traditional alloy in manufacturing process demands while offering improved ductility and impact strength.