David Schwam

The Magnesium Powertrain Cast Components (MPCC) Project is an effort, jointly sponsored by the U.S. Department of Energy and the U.S. Automotive Materials Partnership (USAMP), to demonstrate the readiness of magnesium for use in powertrain applications by testing a set the magnesium-intensive engines which were designed, cast, and assembled. A second MPCC goal is to promote new and strengthen existing magnesium scientific research in North America. The project investigated several of the newly developed high-temperature (creep-resistant) magnesium alloys, which will potentially experience service conditions in the temperature range of 150–200°C and about 50–110 MPa in stresses (typical powertrain). However, the mechanical and physical behaviors of these new alloys are not fully understood. This article outlines MPCC-supported fundamental scientific research into the workings of these new alloys. The areas of research are: phase equilibrium and computational thermodynamics, creep deformation mechanisms, corrosion, hot tearing, and alloy recycling.

This review presents research in the area of polymeric coatings developed for protecting low earth orbit (LEO) space structures from atomic oxygen. Following a brief description of the LEO environment, ground-based simulation facilities for atomic oxygen and evaluation of protective coatings are discussed. Atomic oxygen resistant coatings based on different polymeric systems such as fluorinated polymers, silicones, poly (carborane-siloxane)s and decarborane-based polymers are presented. Finally, the performances of different coating systems are compared and the scope for further research to improve the performance of some of the coating systems is discussed.

The present generation of satellites has a life expectancy limited to 3–5 years, often as a result of environmentally induced degradation of the structural materials. Far from being just inert vacuum, low Earth orbit contains reactive atomic oxygen, an increasing quantity of man made debris, natural micrometeorides, ultraviolet radiation and large temperature extremes. As a result of the synergistic effect of these factors, most polymers and polymer matrix composites degrade rapidly. Atomic oxygen resistant coatings are required to protect them. Flexible protective coatings for solar arrays, fiberglass structural elements and silver interconnects have been designated as a critical technology deficient area. In response to this need, a number of protective siloxane and carborane (siloxane) coating systems were developed and evaluated. The results of the Limited Duration Candidate Exposure flight experiment for these coatings are described. The addition of the carborane is essential in preventing cracking of the coating upon oxidation. Due to its unique structure, each carborane unit can incorporate up to 15 oxygen atoms. This gain offsets the shrinkage caused by carbon loss and densification as the upper layer of the coating turns into a silicate or borosilicate glass. No cracking of the carborane (siloxane) coating was detected, in contrast to the siloxane that cracks upon oxidation. Surface analysis of coatings exposed to the low earth orbit environment demonstrates the formation of a glassy borosilicate layer that provides excellent protection to the substrate.

The durability of materials in molten aluminum is an important consideration in engineering applications such as die casting, containment of liquid metal and semi-solid processing [1]. Die casting is the process of choice in many manufacturing industriesautomotive, ...

A test that involves immersion of the potential mod materials for permanent molds has been developed that provides a thermal cycle that is similar to the experienced during casting of aluminum in permanent molds. This test has been employed to determine the relative thermal fatigue resistance of several different types of mold materials. Four commercial mold coatings have been evaluated for their insulating ability, wear resistance and roughness. The results indicate that composition and structure of the mold materials have considerable effect on their thermal fatigue cracking behavior. Irons with a gray iron structure are the most prone to thermal fatigue cracking followed by compacted graphite irons with the least thermal fatigue cracking of the cast irons experienced by ductile iron. The composition of these various irons affects their behavior.

This study was initiated with the installation of a new production size Ube 350 Ton VSC Squeeze Casting Laboratory at Case Western Reserve University. A Lindberg 75kW electrical melting furnace was installed alongside. The challenge of installation and operation of such industrial-size equipment in an academic environment was met successfully. This investigation has studied the influence of the various casting variables on the quality of indirect squeeze castings primarily of aluminum alloys. The variables studied include gating design, fill time and fill pattern, metal pressure and die temperature variations. The quality of the die casting was assessed an analysis of both their surface condition and internal soundness. The primary metal tested was an aluminum 356 alloy.

... Some of the graphite molds evaluated in this study were machines as cost-share by Hayes Lemmerz. The technical support and advise from Mr. Chad Bullock and Bernie Jaeger of Hayes Lemmerz is gratefully acknowledged. Assistance with filters ...

... Some of the graphite molds evaluated in this study were machines as cost-share by Hayes Lemmerz. The technical support and advise from Mr. Chad Bullock and Bernie Jaeger of Hayes Lemmerz is gratefully acknowledged. Assistance with filters ...

ABSTRACT The need to produce lighter components in transportation equipment is the main driver in the increasing demand for magnesium castings. In many automotive applications, components can be made of magnesium or aluminum. While being lighter, often times the magnesium parts have lower impact and fatigue properties than the aluminum. The main objective of this study was to identify potential improvements in the impact resistance of magnesium alloys. The most common magnesium alloys in automotive applications are AZ91D, AM50 and AM60. Accordingly, these alloys were selected as the main candidates for the study. Experimental quantities of these alloys were melted in an electrical furnace under a protective atmosphere comprising sulfur hexafluoride, carbon dioxide and dry air. The alloys were cast both in a permanent mold and in a UBE 315 Ton squeeze caster. Extensive evaluation of tensile, impact and fatigue properties was conducted at CWRU on permanent mold and squeeze cast test bars of AZ91, AM60 and AM50. Ultimate tensile strength values between 20ksi and 30ksi were obtained. The respective elongations varied between 25 and 115. the Charpy V-notch impact strength varied between 1.6 ft-lb and 5 ft-lb depending on the alloy and processing conditions. Preliminary bending fatigue evaluation indicates a fatigue limit of 11-12 ksi for AM50 and AM60. This is about 0.4 of the UTS, typical for these alloys. The microstructures of the cast specimens were investigated with optical and scanning electron microscopy. Concomitantly, a study of the fracture toughness in AM60 was conducted at ORNL as part of the study. The results are in line with values published in the literature and are representative of current state of the art in casting magnesium alloys. The experimental results confirm the strong relationship between aluminum content of the alloys and the mechanical properties, in particular the impact strength and the elongation. As the aluminum content increases from about 5% in AM50 to over 9% in AZ91, more of the intermetallic Mg17Al12 is formed in the microstructure. For instance, for 15 increase in the aluminum content from AM50 to AM60, the volume fraction of eutectic present in the microstructure increases by 35%! Eventually, the brittle Mg17Al12 compound forms an interconnected network that reduces ductility and impact resistance. The lower aluminum in AM50 and AM60 are therefore a desirable feature in applications that call for higher impact resistance. Further improvement in impact resistance depends on the processing condition of the casting. Sound castings without porosity and impurities will have better mechanical properties. Since magnesium oxidizes readily, good melting and metal transfer practices are essential. The liquid metal has to be protected from oxidation at all times and entrainment of oxide films in the casting needs to be prevented. In this regard, there is evidence that us of vacuum to evacuate air from the die casting cavity can improve the quality of the castings. Fast cooling rates, leading to smaller grain size are beneficial and promote superior mechanical properties. Micro-segregation and banding are two additional defect types often encountered in magnesium alloys, in particular in AZ91D. While difficult to eliminate, segregation can be minimized by careful thermal management of the dies and the shot sleeve. A major source of segregation is the premature solidification in the shot sleeve. The primary solid dendrites are carried into the casting and form a heterogeneous structure. Furthermore, during the shot, segregation banding can occur. The remedies for this kind of defects include a hotter shot sleeve, use of insulating coatings on the shot sleeve and a short lag time between pouring into the shot sleeve and the shot.