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Joining dissimilar parts in automotive interior trim applications has been accomplished by utilizing mechanical fasteners, organic and water based adhesives, and more recently, thermoplastic polymers. Recent trends towards reducing solvent emissions and waste management problems, improving the consistency of adhesive application, integrating parts, lowering parts fabrication costs, and designing a specified bond level has increased the use of thermoplastic adhesive films as bonding agents in several applications. Initial efforts began over fifteen years ago with Dow Adhesive Films (DAF) being designed for bonding interior trim fabrics to various substrates. Films have subsequently been designed to improve performance of many interior trim parts in many ways such as: improving water resistance, allowing the part to be molded before installation, imparting a slip surface to a part, and supporting a non-woven fabric.

The persistent occurrence of microporosity defects in AZ91 castings has made it difficult to consistently produce sound parts. Earlier work established that dissolved hydrogen gas causes microporosity defects in AZ91; however, the exact role of hydrogen in the nucleation and growth of microporosity was not determined. In this paper, the behavoir of dissolved hydrogen gas in elemental magnesium, AZ91 alloy, and liquid binary Mg/Al alloys was studied. The results show that during the last stages of solidification, hydrogen gas is rejected from the Mg17Al12 intermetallic compound to assist in the nucleation and/or growth of microporosity.

The effect of non-metallic inclusions (NMIs) on the properties of die cast magnesium was investigated. NMI content was quantified by a newly developed light reflectance technique. The mechanical properties of optimized AM60B test bars were found to decrease at high inclusion levels. Low inclusion levels did not statistically reduce the mechanical properties of AM60B as compared to virgin metal. Argon-refined AM60B displayed mechanical properties that were indistinguishable from virgin alloy. AZ91D test plates were die cast at various cleanliness levels. After salt spray testing, it was found that the surface quality of the castings was slightly degraded at high NMI levels. The general corrosion performance was also affected, but paint adhesion was relatively unaffected. At high NMI levels, the corrosion performance was still better than 380 A. Machinability of the AZ91D test plates was quantified by measuring tool wear and cutting forces.

With the introduction of high purity corrosion resistant magnesium alloys and also the re-emphasis of quality products throughout the industrial world, the need for more accurate and more reproducible analysis between laboratories has become apparent. The availability of high quality analytical standards was one of the principle obstacles to achieving analytical agreement between laboratories. This presentation briefly reviews what until recently was available to the industry and their customers with respect to analytical methods and analytical standards and their limitations in today's quality conscious world. The development of a new series of die cast magnesium standards by The Dow Chemical Company is also described in this paper including their compositional design considerations relating to the selection of the modern direct reading emission spectrometer as the analytical instrument of choice.

The magnesium alloy AE42 (nominally a 4 % aluminum, 2 % rare earth alloy of magnesium) is a developmental die cast alloy with good strength and creep resistance at elevated temperatures. Standard salt spray corrosion tests have been used with controlled purity AE42 die castings to define the critical iron, nickel and copper contaminant levels below which excellent corrosion performance can be obtained. As previously observed with the magnesium alloys AZ91, AM60, and AS41, the critical iron content is dependent upon the manganese content of the alloy. While the iron:manganese tolerance for AE42 is about the same as that of AM60, the tolerance for the nickel and copper contaminants is greater than that of AZ91. When each of these contaminants is less than the critical level, the salt spray performance was equal to or better than die cast 380 aluminum and cold rolled steel.

Recent growth in automotive applications of magnesium die cast alloys has made the refining and recycling of magnesium scrap a key issue for the automotive and magnesium industries, if growth is to continue. Today, with only a few exceptions, commercially refined and recycled alloy is produced using a variety of flux-based processes. However, fluxless refining, has been the focus of growing interest, particularly for the in-house refining of scrap by the die cast producers. This paper summarizes the results of a study conducted to better understand the behavior of non-metallic contaminants in scrap melts and the requirements for their separation, using argon sparging. Brightness measurements were used to experimentally determine the distribution of non-metallic contaminants within scrap melts both before and after argon treatment.

A method for refining magnesium scrap which produces consistent, high quality magnesium metal has been developed. High quality magnesium metal is defined in this paper as metal which has heavy metal contaminants controlled within high-purity ASTM chemical specification, and is relatively free of internal impurities such as non-metallic inclusions (oxides and flux) and dissolved gas. The refining process utilizes a protective gas atmosphere, inert gas sparging and filtration techniques, rather than salt based fluxes, to remove both non-metallic inclusions and dissolved gases. Experimentation results of this refining process indicate magnesium scrap can be remelted and refined to a quality equal to or better than virgin ingot, without the introduction of salt based fluxes or a large capital investment.

The relationship between hydrogen gas and microporosity in magnesium alloy AZ91 was quantified, refuting the belief that hydrogen levels less than the maximum solid solubility are of no detriment. Sand castings were made from melts containing measured levels of hydrogen gas, and the amount of porosity was determined by density measurements. At concentrations below the maximum solid solubility, it was established that the amount of microporosity is directly proportional to the gas content. This supports the premise that dissolved hydrogen gas provides nucleation sites for microporosity, and that it is useful to remove all gas to achieve porosity-free cast parts.

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.

Standard salt spray corrosion tests have been used with controlled purity AM60 castings to define the critical iron, nickel, and copper contaminant levels below which excellent corrosion performance can be obtained. As previously observed with the AZ91 alloy, the iron solubility and the corrosion tolerance limit for iron are dependent upon the manganese content of the metal. The zinc free AM60 alloy has a somewhat lower tolerance for all three of the critical contaminants when compared to AZ91, but when the three contaminants are below their individual tolerance limits, the salt spray performance is again equal to or better than die cast 380 aluminum and cold rolled steel.

New efforts to improve quality control through the use of Statistical Quality Control techniques were introduced to the Dow Magnesium Extraction Process. All the employees in the magnesium plants were trained in the Statistical Quality Control procedures. Successful application has lead to improved chemical purity and reduced variability in the feed process. These improvements were followed by better reduction cell operation, improvements in alloying and casting operations. Consistent quality, high purity magnesium alloys are now available for use in automotive applications.

The market for composite engine oil sealing components, such as valve covers and oil pans, continues to expand, replacing traditional metal stamping and die casting materials. As the market for these composite components grows, so must the understanding of the material performance characteristics and the relationship of these characteristics to the design of the part. Unlike metals, composites are viscoelastic in nature, exhibiting time-temperature dependant properties. Therefore, the traditional design approach utilizing static property data to predict long-term performance under load and over a wide temperature range will not sufficiently characterize the nonlinear property response of polymeric-based composites. A robust composite sealing design requires complete materials characterization, including long-term creep performance as a function of temperature, loading, and cycling.

The construction of most automotive interior headliners requires an adhesive material to bond polyurethane foam-backed fabric to a molded headliner shell. More than ten years ago, The Dow Chemical Company qualified and began supplying a thermoplastic adhesive polymer film for headliner applications which replaced wet adhesive systems at several fabricators. DAF 899 adhesive film has gained acceptance in the industry due to excellent performance, convenience, and cost effectiveness without additional waste handling or volatile organic emission concerns. Recent advancements in headliner design such as additional recessed areas with more demanding contours, new substrate materials and the desire for more efficient operations created an opportunity to design improved adhesive films to meet the emerging industry demands.

Fast, accurate delivery of metal to the shot well is critical to the success of any cold chamber die casting operation. For some metals this is a simple problem to solve. Magnesium, however, requires more innovative thinking. Simplicity of design is essential for reliable operation in the environment of a magnesium die casting facility. Complex control is required to provide speed and accuracy of shot delivery. Blending these two ingredients to produce a viable system produces a truly innovative shot delivery system for magnesium. Construction details of a newly developed stand alone system for the auto ladling of magnesium will be presented. Data with regard to speed and accuracy will also be presented.

Adhesive materials are required to bond cover fabrics to most molded interior headliner substrates. Several thermoplastic adhesive films are qualified and used at U.S. and Japanese OEM's. These adhesive films offer benefits such as convenience, cost effectiveness, excellent adhesive performance and process efficiency while reducing concerns of emissions and hazardous waste handling compared to prior bonding methods. The automotive headliner part is a multifunctional component of the vehicle's interior trim. One of the main headliner functions is to reduce the interior cabin noise. Various adhesive materials are used in a lamination process to form a composite headliner. The purpose of this study was to compare the effects of this lamination process and various alternative adhesive materials on the overall acoustical performance of the headliner composite. Various headliner samples were fabricated under controlled process conditions and tested by an independent acoustics testing lab.