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L I t E r A t U r E S E r v I C E
Kombination von Konstruktion, Gießverfahren und Werkstoff
gefordert. Untersuchungen zum Einsatz geeigneter Zylinderkopflegierungen
haben gezeigt, dass die Legierung allein die
Forderungen nicht erfüllen kann. Ein funktionierendes Bauteil
erhält man nur durch geeignete Konstruktion und ein werkstoffgerechtes
Herstellungsverfahren. Dies beinhaltet neben dem
Gießen vor allem auch die Wärmebehandlung. Bei den Bauteilfestigkeiten
ist zu beobachten, dass die nominellen statischen
Werte durch Eigenspannungen – z.B. aus der Warmbehandlung
– überlagert werden können. Dies kann dazu führen, dass das
nominelle Potenzial des Werkstoffs nicht immer genutzt wird.
13 Abb., 3 Tab.
ALUMINIUM 9 (2009) Anwendung
R. A. P. Fielding
homogenization of Aluminium Alloy Extrusion Billet
Part iii: The Application of the Continuous
homogenization Process to AA6xxx Series Alloys
Light Metal Age, April 2009, S. 8-17
The majority of AA6xxx extrusion alloy billets are homogenized
in one of the 90 continuous furnaces manufactured by Hertwich
Engineering since their first prototype was supplied to
Amag in Austria in 1980. The advantages of this technology
and issues specific to the design, operation and control of these
furnaces are discussed. The productivity and, to a large degree,
the recovery from the extrusion of an aluminium alloy billet
is dependent on its thermal history from alloying and casting
through homogenization until its entry to the extrusion die. As
was pointed out by Reiso, an optimum billet structure for one
extruder may not be the optimum for another. Whether a prime
or a secondary producer supplies the extrusion billet, variations
in the chemical composition, the preparation of the melt,
or the casting and homogenization processes, can be detected
at the extrusion press. Additionally, in the extrusion plant, the
specific pressure of the presses and the design of the extrusion
dies affect the choice of die, billet and container temperatures.
The rate of heating the billet before entering the extrusion press
varies between induction and gas-fired furnaces. All of these
factors have an influence on the optimum billet structure. As a
consequence, the production of extrusions, from molten metal
to the age ovens, must be looked upon as a whole. What happens
at one stage of the production process is not independent of the
other stages. 5 figures, 27 sources
ALUMINIUM 9 (2009) Strangpressen
J. C. LaBelle, T. Dolby
hex Washer-head Fastener
Pull-Over in Moderately Thin Aluminium
Light Metal Age, April 2009, S. 40-43
Pull-over, also termed pull-through, is a mode of failure for a
tension-loaded fastener in which the sheet, plate or extrusion
locally tears and/or deforms sufficiently to allow the head to
pass completely through. Screws are used to resist tensile design
loads in a variety of aluminium structures including skylights,
curtain walls, and window framing. The Aluminium Design
Manual (ADM) includes equation 5.4.2.2-1 for pull-over of tapping
screws installed in aluminium. This formula, however, was
based on testing of relatively thin aluminium, 1.02 mm (0.040“)
maximum, using hex-head fasteners with loose washers that
were a metal/rubber combination. Subsequently, limited testing
indicated that this equation was likely conservative for greater
thicknesses. Thus, a testing programme was initiated in order to
study behaviour and provide design guidance for the pull-over
mode for hex-head screws with integral or loose metal-washers,
and pan-head screws, installed in moderately thin aluminium.
Thicknesses ranged from about 1.02 mm (0.040“) to 6.35 mm
(0.25“). Testing covered a range of fastener-plate combinations
(sets) including four screw diameters, five plate thicknesses, and
several alloy-tempers. In total, 162 specimens were tested (Fig.
1), usually with eight tests for each combination (set) of screw
size, plate thickness, and alloy-temper. Pull-over occurred in all
of the tests except for those with nominal 6.35 mm (1/4“) thick
plates. In these tests, screw failure occurred.
Data analysis included comparisons between test results and
predicted (nominal) values based on the ADM. In all cases, the
ADM pull-over prediction was substantially less than the test
average for the new data. A simple design equation was developed
to more accurately, yet conservatively, model pull-over
behaviour for screws installed in aluminium with a minimum
thickness of 1.02 mm (0.040“) and prescribed hole sizes. 4 figures,
5 tables, 7 sources.
ALUMINIUM 9 (2009) Verarbeitung, erste Stufe
Sh. Akhtar, G. Timelli, F. Bonollo, L. Arnberg, M. Di Sabatino
A comparative study of defects and mechanical properties in
high pressure die cast and gravity die cast aluminium alloys
International Foundry Research/Giessereiforschung 61 (2009)
No. 2, S. 36-48
Defects such as pores, hot tears, entrained oxides or macrosegregation
may occur in aluminium die castings, impairing their
mechanical properties. The nature, extent and distribution of
such defects will, however, differ between die casting processes.
To investigate these differences, a comparative study between
gravity castings of an A356 alloy and high pressure die castings
of an A380 alloy was carried out. The defect distributions of
the castings were investigated by metallography, radiography
and fractography, and the tensile properties were measured.
The gravity die castings were produced in a step mould with
and without filter and at different controlled hydrogen concentrations
in the melt. The U-shaped pressure die castings were
produced with systematic variations of process parameters
such as plunger speed, commutation point between first and
second phase and pouring temperature. It has been found that
both castings contain defects, primarily pores and oxides, and
that the presence and distribution of these defects are highly
sensitive to the process conditions. Significant variations of the
defect distribution have, however, also been found in castings
produced under the same conditions, particularly in the pressure
die castings indicating the stochastic nature of defects in
die castings. The dominating defect type in the gravity die casting
is hydrogen porosity mainly at high hydrogen melt concentrations,
whereas in the high pressure die castings, oxides and
entrapped air porosity dominate. The tensile properties in both
types of castings are affected by the amount and distribution of
defects. This effect is particularly prominent for the pressure
die castings where the defect area fraction has been found to
determine the tensile strength. In the gravity castings, hydrogen
porosity decreases the tensile strength, but this effect becomes
significant only at quite high hydrogen melt concentrations. The
tensile properties as well as the porosity also depended on the
cross section of the castings. 26 figures, 4 tables, 27 sources
ALUMINIUM 9 (2009) Formguss, Gusslegierungen
Für Schrifttum zum Thema „Aluminium“ ist der Gesamtverband der Aluminiumindustrie e.V. (GDA)
der kompetente Ansprechpartner. Die hier referierten Beiträge repräsentieren lediglich einen Ausschnitt
aus dem umfassenden aktuellen Bestand der GDA-Bibliothek.
Die von der Aluminium-Zentrale seit den dreißiger Jahren kontinuierlich aufgebaute Fach-Bibliothek
wird duch den GDA weitergeführt, ausgebaut und auf die neuen Medien umgestellt. Sie steht allen
interessenten offen.
Ansprechpartner ist Dr. Karsten hein, E-Mail: karsten.hein@aluinfo.de
62 ALUMINIUM · 9/2009