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Technical Paper

Semi-Solid Casting of Magnesium and Aluminum Alloys via the CRP (Continuous Rheo-conversion Process)

2006-04-03
2006-01-0509
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.
Technical Paper

Development Techniques for Automotive Cast Components

2006-04-03
2006-01-0512
This paper outlines the development process for cast components used in structural automotive applications. Typical design characteristics such as STRENGTH, STIFFNESS, CRASHWORTHINESS, FATIGUE and manufacturability for COST are discussed. Appropriate methods for material selection, part consolidation, development process and tools, product specification and nondestructive testing, prototype and product validation testing are covered in details. As aluminum alloys are the most commonly used lightweighting materials, the VRC/PRC process, invented by Alcoa, will be used in most of the case studies presented. This article constitutes a reference for design engineers and purchasing engineers to select material and manufacturing process that best suit their applications based on cost and performance.
Technical Paper

Notched Bar Izod Impact Properties of Zinc Die Castings

2006-04-03
2006-01-0513
Notched bar Izod impact testing of zinc die cast Alloy 3, Alloy 5, ZA-8, and AcuZinc 5 was performed at five temperatures between -40 °C and room temperature in accordance with ASTM E23 for impact testing of metallic materials. A direct comparison between ASTM D256 for impact testing of plastics and ASTM E23 was performed using continuously cast zinc specimens of Alloy 5 and ZA-8 at -40 °C and room temperature. There are differences in sample sizes, impact velocity, and striker geometry between the two tests. Bulk zinc tested according to ASTM E23 resulted in higher impact energies at -40 °C and lower impact energies at room temperature then did the same alloys when tested according to ASTM D256.
Technical Paper

Rational Selection of Mg Concentration Specifications for 319-Type Alloys

2006-04-03
2006-01-0511
Previous studies on the effect of Mg on the hardness of 319-type alloys are contradictory. The present study was conducted in an attempt to resolve this confusion and allow for a more rational choice of Mg concentration specifications. Four 319-type alloys were prepared with the following target Mg concentrations: 0.00, 0.15, 0.35 and 0.45 wt%. The addition of only 0.15 wt% Mg had a significant effect on the hardness of the alloy but further incremental additions of Mg did not produce the expected trends in hardness. Two hypotheses for this unexplained behavior are presented. This work suggests that the Mg concentration can be allowed to vary between 0.15 wt% and 0.45 wt% without significantly impacting the aging response (hardness) of the alloy.
Technical Paper

Production Uses of Computed Tomography - Samples in an Aluminum Foundry

2006-04-03
2006-01-0510
Cast parts are traditionally inspected prior to initial production runs and subsequently in support of high volume production to ensure consistent quality and accurate dimensions that match the “as designed” part within specified tolerances. Classical methods for dimensional measurements are CMM systems using touch probes, laser sensors, or optical techniques. Flaw conditions such as cracks, porosity and inclusions can be detected with “real-time” x-ray inspection. These techniques are quite effective on simple parts with two dimensional geometry and non-complicated structures. Specialized x-ray inspection systems for alloy wheel production are examples of such systems. Complex three dimensional castings such as cylinder heads and engine blocks have functional internal structures with close tolerances and morphology that cannot be verified by CMM systems externally or by real-time x-ray.
Technical Paper

Quick Plastic Forming of a Decklid Inner Panel with Commercial AZ31 Magnesium Sheet

2006-04-03
2006-01-0525
Experimental quick plastic forming (QPF) of commercially available magnesium alloy AZ31B sheet into Cadillac STS decklid inner panels was done successfully with existing QPF tools and processes developed for forming QPF-grade AA5083 aluminum sheet. This demonstrates that QPF parts designed for aluminum can be made with magnesium. The post-formed properties of the formed panel were investigated. Thinning of the magnesium alloy sheet in the successfully formed panel was limited to just under 50%, which is normally considered acceptable in QPF aluminum panels. The basal crystallographic texture of the sheet material was essentially maintained through the forming process. Tensile properties of samples cut from the formed panels exceed the specified minimums for the O-temper AZ31 sheet. Significant reduction in cycle time is expected based on the results of this work.
Technical Paper

The USAMP Magnesium Powertrain Cast Components Project

2006-04-03
2006-01-0522
Over the past five years, the US Automotive Materials Partnership (USAMP) has brought together representatives from DaimlerChrysler, General Motors, Ford Motor Company and over 40 other participant companies from the Mg casting industry to create and test a low-cost, Mg-alloy engine that would achieve a 15 - 20 % Mg component weight savings with no compromise in performance or durability. The block, oil pan, and front cover were redesigned to take advantage of the properties of both high-pressure die cast (HPDC) and sand cast Mg creep- resistant alloys. This paper describes the alloy selection process and the casting and testing of these new Mg-variant components. This paper will also examine the lessons learned and implications of this pre-competitive technology for future applications.
Technical Paper

The Effect of Porosity on the Microstructure and Mechanical Properties of Die Cast Mg Alloys

2006-04-03
2006-01-0524
High pressure die casting (HPDC) is the dominant process for the production of magnesium components with complex configuration having typically thin to medium wall thickness. The growing use of die cast Mg alloys in the automotive industry, particularly for the production of drive-train components, has led to the development of creep resistant alloys, MRI153M and MRI230D, which were launched into the market several years ago. The present paper aims at exploring the effect of the HPDC process parameters on the porosity and, as a result, on the properties of the two MRI's developed alloys in comparison with common alloys AZ91D and AM50A that are usually considered as benchmark die casting alloys. The outcome of the research performed includes processing guidelines and recommendations, which allow obtaining high quality sound castings. These recommendations should be implemented in the course of design, optimization and production of high-performance components for various applications.
Technical Paper

Lightweight Magnesium Intensive Body Structure

2006-04-03
2006-01-0523
This paper describes a lightweight magnesium intensive automobile body structure concept developed at DaimlerChrysler to support a high fuel-efficiency vehicle project. This body structure resulted in more than 40% weight reduction over a conventional steel structure while achieving significantly improved structural performance as evaluated through CAE simulations. A business case analysis was conducted and showed promising results. One concept vehicle was built for the purpose of demonstrating concept feasibility. The paper also identifies areas for further development to enable such a vehicle to become a production reality at a later time.
Technical Paper

Galvanic Corrosion of Die Cast Magnesium Exposed on Vehicles and in Accelerated Laboratory Tests

2006-04-03
2006-01-0255
Galvanic corrosion between die cast AZ91D and AM60B and different fastener systems has been evaluated by exposure on trucks and in accelerated laboratory tests. The exposure time on the trucks was 3 years, corresponding to a mileage of about 300000 km. Samples were retracted and evaluated after 1 and 2 years exposure. Similar samples were also exposed to the Volvo Indoor Corrosion Test and the General Motors GM9540P-cycle B test. The correlation between the field data and the laboratory tests was evaluated, as was the sharp difference in the performance of the fastener systems in the two accelerated laboratory tests.
Technical Paper

Influence of the Copper Content on Microstructure and Corrosion Resistance of AZ91 Based Secondary Magnesium Alloys

2006-04-03
2006-01-0254
Copper is one of the critical elements that can enrich in Mg alloys during recycling of post consumer scrap. Sources of copper are coatings on used magnesium parts or aluminium alloy contaminations in Mg scrap. Therefore, it is important for the development of secondary magnesium alloys to understand the effects of copper in the microstructure of magnesium AZ based alloys and how this influences the corrosion resistance. Copper contents have been varied between 0 and 2 wt% in gravity die cast AZ91D alloy. The resulting microstructures were studied by LM, SEM + EDX and XRD. Already at low Cu contents (0.25 wt% Cu) ternary Mg-Al-Cu intermetallic phases were observed. Further increasing Cu concentrations resulted in more copper-rich phases, and a significantly reduced corrosion resistance was found. By correlating microstructure and corrosion properties, critical Cu concentrations were defined and corrosion minimising strategies for AZ based secondary alloys were developed.
Technical Paper

Hot Rolling of AZ31 Magnesium Alloy to Sheet Gauge

2006-04-03
2006-01-0259
This study details preliminary results of hot rolling trials of AZ31 alloy sheet using a pilot-scale rolling mill. The aim is to design and optimize the hot rolling schedule for AZ31 in order to produce sheet with a fine and homogeneous microstructure. The study examined three different hot rolling temperatures, 350, 400 and 450°C and two rolling speeds, 20 and 50 RPM. A total thickness reduction of 67% was obtained using multiple passes with reductions of either 15% or 30% per pass. The entry temperature of each rolling schedule was kept constant, by reheating the strip between passes. It was found that the microstructure of the AZ31 alloy was sensitive to the rolling temperature, the reduction (i.e. strain) per pass and the rolling speed (i.e. strain rate). A combination of a rolling temperature of 400°C, reduction per pass of 15%, and rolling speed of 50 RPM produced the finest and most homogeneous microstructure.
Technical Paper

Effect of Temperature and Strain Rate on Formability of AZ31 Magnesium Sheet Alloy

2006-04-03
2006-01-0258
The deformation characteristics of a commercial AZ31 magnesium sheet alloy were investigated at elevated temperatures. Tensile experiments were conducted at temperatures 300°C, 400°C and 450°C and at strain rates, 0.001s-1, 0.01s-1 and 0.1s-1. Depending on the test temperature, fracture analysis of failed specimens revealed three different types of failure: (1) by moderate necking, (2) by interlinkage cavity, (3) by strong necking. Plastic strain ratios, r-values were derived from the strain ratios of width and thickness of the fractured tensile specimens. The r-value increased with increasing temperature and strain rate.
Technical Paper

Aqueous Corrosion of Experimental Creep-Resistant Magnesium Alloys

2006-04-03
2006-01-0257
This paper presents a comparison of aqueous corrosion rates in 5% NaCl solution for eight experimental creep-resistant magnesium alloys considered for automotive powertrain applications, as well as three reference alloys (pure magnesium, AM50B and AZ91D). The corrosion rates were measured using the techniques of titration, weight loss, hydrogen evolution, and DC polarization. The corrosion rates measured by these techniques are compared with each other as well as with those obtained with salt-spray testing using ASTM B117. The advantages and disadvantages of the various corrosion measurement techniques are discussed.
Technical Paper

Corrosion Fatigue of AM50 and AE44 Alloys at Various Temperature and R-Ratio

2006-04-03
2006-01-0256
Reported in this paper are the experimental results obtained from corrosion fatigue tests of high pressure die cast (HPDC) AM50 and AE44 magnesium specimens immersed in NaCl and GM9540P solutions at various temperature, low and high R-ratio. Test specimens were loaded under cyclic loading at temperature of −5°, 25°, and 80°C. It is shown that fatigue life was reduced significantly in these corrosive environments. Although the fatigue life (in air) is longer for specimens tested in −5°C in comparison with the ambient temperature data, the relative reduction of fatigue life in corrosive environments is much significant than that at 25°C. An investigation of the effect of stress level on AM50 fatigue life shows that, for R=0.1, there is more loss in fatigue life, due to corrosion, when the applied stress is low; when the applied maximum stress is above the yield point, the reduction in fatigue life is relatively less significant.
Technical Paper

Effect of Bolt CTE on Bolt Load Retention for Mg Alloys

2006-04-03
2006-01-0071
The automobile and light truck industries are increasing considering the use of magnesium castings in structural and elevated-temperature applications. Unfortunately, the bolt load compressive stress retention behavior of magnesium alloys is unacceptable for most elevated temperature applications. In this investigation, the effects of bolt strength and the mis-match in the coefficient of thermal expansion (CTE) of magnesium alloy AZ91D and the bolt material has been determined for a wide range of materials (martensitic steel, austenitic stainless steel, ductile iron and aluminum alloys). Also, the effect of heat treating the magnesium alloy, the effect of re-tightening the bolts after the first thermal cycle and the maximum load carry capacity of numerous bolt materials were determined. Corrosion was not considered.
Technical Paper

Bolt-load Retention Testing of Magnesium Alloys for Automotive Applications

2006-04-03
2006-01-0072
For automotive applications at elevated temperatures, the need for sufficient creep resistance of Mg alloys is often associated with retaining appropriate percentages of initial clamp loads in bolt joints. This engineering property is often referred to as bolt-load retention (BLR); BLR testing is a practical method to quantify the bolt load with time for engineering purposes. Therefore, standard BLR test procedures for automotive applications are desired. This report summarizes the effort in the Structural Cast Magnesium Development (SCMD) project under the United States Automotive Materials Partnership (USAMP), to provide a technical basis for recommending a general-purpose and a design-purpose BLR test procedures for BLR testing of Mg alloys for automotive applications. The summary includes results of factors influencing BLR and related test techniques from open literature, automotive industry and research carried out in this laboratory project.
Technical Paper

The European Union Mg-Engine Project - Generation of Material Property Data for Four Die Cast Mg-Alloys

2006-04-03
2006-01-0070
A specific objective of the European Mg-Engine project is to qualify at least two die cast Mg alloys with improved high temperature properties, in addition to satisfactory corrosion resistance, castability and costs. This paper discusses the selection criteria for high temperature alloys leading to four candidate alloys, AJ52A, AJ62A, AE44 and AE35. Tensile-, creep- and fatigue testing of standard die cast test specimens at different temperatures and conditions have led to a very large amount of material property data. Numerous examples are given to underline the potential for these alloys in high temperature automotive applications. The subsequent use of the basic property data in material models for design of automotive components is illustrated.
Technical Paper

BMW's Magnesium-Aluminium Composite Crankcase, State-of-the-Art Light Metal Casting and Manufacturing

2006-04-03
2006-01-0069
This paper presents new aspects of the casting and manufacturing of BMWs inline six-cylinder engine. This new spark-ignition engine is the realization of the BMW concept of efficient dynamics at high technological level. For the first time in the history of modern engine design, a water-cooled crankcase is manufactured by magnesium casting for mass production. This extraordinary combination of magnesium and aluminium is a milestone in engine construction and took place at the light-metal foundry at BMW's Landshut plant. This paper gives a close summary about process development, the constructive structure, and the manufacturing and testing processes.
Technical Paper

Machinability of MADI™

2005-04-11
2005-01-1684
High strength materials have desirable mechanical properties but often cannot be machined economically, which results in unacceptably high finished component cost. MADI™ (machinable austempered ductile iron) overcomes this difficultly and provides the highly desirable combination of high strength, excellent low temperature toughness, good machinability and attractive finished component cost. The Machine Tool Systems Research Laboratory at the University of Illinois at Urbana-Champaign performed extensive machinability testing and determined the appropriate tools, speeds and feeds for milling and drilling (https://netfiles.uiuc.edu/malkewcz/www/MADI.htm). This paper provides the information necessary for the efficient and economical machining of MADI™ and provides comparative machinability data for common grades of ductile iron (EN-GJS-400-18, 400-15, 450-10, 500-7, 600-3 & 700-2) for comparison.
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