The effect of processing parameters on the tensile properties of alumina fiber reinforced magnesium
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INTRODUCTION
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previous study of the fatigue and tensile behavior of unidirectional FP AI:O3 fiber-reinforced metal matrix composites with either a commercially pure (CP) magnesium or a ZE41A magnesium alloy (Mg-4.25Zn-0.5Zr- 1.25RE) matrix has revealed a dramatic strengthening effect accompanying the alloy additions. 1The alloy additions were found to improve the off-axis properties but decrease the axial properties, due to both an increase in the matrix and interfacial strengths and a decrease in the fiber strength. The differing mechanical behavior was accompanied by a differing off-axis failure mode between the two materials. In the CPMg material, off-axis failure occurred parallel to the fiber orientation in all orientations studied (22.5, 45, and 90 deg). 2 In the stronger ZE41A material off-axis failure was a combination of failure across and along the fibers, up to an orientation of 45 deg. The differing failure modes and higher off-axis strength indicated an improved inteffacial strength in the ZE41A. It was originally hypothesized that the alloying elements in ZE41A did not directly contribute to the improved interracial strength, since Auger electron spectroscopy (AES) revealed that there was no segregation of alloying or impurity elements to the fiber-matrix interface region. Transmission electron microscopy (TEM) showed that the fiber-matrix reaction zone in both CPMg and ZE41A was composed of MgO particles, although the MgO particles in the ZE41A were approximately twice as large as those found in the CPMg. Based on these results, it was suggested that the interfacial strengthening in the ZE41A was due to the increased size of the reaction zone and/or the change in the size and spacing of the MgO crystals, and not to any change in the chemical nature of the reaction zone. It was postulated that this larger reaction zone resulted from A. McMINN and R.A. PAGE, Senior Research Metallurgists, and W. WEI, Research Metallurgist, are with Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78284. Manuscript submitted July 1, 1986.
METALLURGICAL TRANSACTIONS A
a longer contact time with the highly reactive liquid matrix during processing, due to differences in the solidification behavior of the two matrices) The implications from this previous work were that, by properly modifying the casting conditions, improved properties could be obtained for CPMg without the expense of alloying element additions. It has been shown that, by heating CPMg samples above the melting point of the matrix, the MgO precipitate size increased with increasing contact time between the molten matrix and the A1203 fibers.3 There was also an increase in the amount of Mg matrix adhesion to the fibers with increasing contact time. However, whether there was any improvement in interfacial strength was not determined. This paper reports the results of a continued study of the effect of processing variables on the tensile properties of FP A1203 fiber reinforced CPMg. E. I. DuPont de Nemours and Co. changed their normal p
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