Browsing by Author "Weiss, D"

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    In situ neutron diffraction solidification analyses of rare earth reinforced hypoeutectic and ypereutectic aluminum–silicon alloys
    (The Minerals, Metals & Materials Society, 2020-02-24) Stroh, J; Sediako, D; Weiss, D; Peterson, VK
    The recognised potential of rare earth (RE) additions such as cerium (Ce) and lanthanum (La) for strengthening aluminium alloys has led to an area of research focused on the development of new alloys, targeting powertrain applications that require high temperature strength and creep resistance. In an attempt to further improve the mechanical properties of the Al–Si system, this paper addresses the effects that RE additions have on the microstructure and phase evolution during solidification. This study presents the results of in situ solidification studies using neutron diffraction and microstructural analyses using scanning electron microscopy with energy-dispersive spectroscopy of Al7Si3.5RE and Al18Si8RE alloys, where numerical notation indicates composition in wt%. We find that the RE additions lead to the formation of globular Al20Ti2(Ce6-LaNd) and rod-like Si3Al2(Ce3La2Nd) intermetallics in the Al7Si3.5RE alloy. We also find that Si and Cu additions in the Al18Si8RE alloy transforms the solid structure of the rod-like Si3Al2(Ce3La2Nd) intermetallic to a fibrous twin-layered material comprised of alternating Si3Ce1Al1(-La6Nd3Cu2Pr) and Al5Si4CeCu(La6Nd3Pr) constituents. Furthermore, the high RE content in the Al18Si8RE alloy leads to a prolonged solidification range which may increase the alloy’s susceptibility to porosity formation.
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    Possible evidence for wet Heinrich phases in tropical NE Australia: the Lynch's Crater deposit
    (Elsevier, 2008-03) Muller, J; Kylander, M; Wust, RAJ; Weiss, D; Martinez-Cortizas, A; LeGrande, AN; Jennerjahn, T; Behling, H; Anderson, WT; Jacobsen, GE
    Unarguably, one of the most significant paleoclimatological discoveries of the last two decades has been that of abrupt climate events (Dansgaard-Oeschger cycles and Heinrich events). Most evidence for these events has originated from the high-latitude Northern Hemisphere.. with few records documenting the response of the low latitude Southern Hemisphere. Here we present new data from Lynch's Crater, a unique terrestrial record from NE-Australia that may show evidence for southward propagations of the Intertropical Convergence Zone (ITCZ) during abrupt climate perturbations as a result of alteration of the low latitude air masses. Proxies for precipitation/wetness indicate enhanced rainfall in the region during Heinrich events (H events 1-3) and the 8.2 ka Northern Hemisphere cold event. A fully coupled atmosphere/ocean climate model simulating a 1 Sv freshwater influx to the North Atlantic Ocean produces a scenario which agrees with the climate changes shown by the Lynch's Crater record. The model shows precipitation anomalies that include a southward migration of the ITCZ and a zonal shift in mid-latitude storm tracks over the Southern Hemisphere equatorial region. These data indicate large-scale shifts of the austral summer ITCZ position that is known to control monsoonal precipitation in NE Australia. This terrestrial record from Australia may demonstrate the involvement of the tropical western Pacific Ocean in ITCZ migrations during abrupt climate events of the last glacial period. Defining such past migrations offers insight into the importance and role of the equatorial region in global climate dynamics. © 2007, Elsevier Ltd.