• Version
• 160 Downloads
• 1.30 MB File Size
• 1 File Count
• November 4, 2016 Create Date
• November 4, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - Corrosion Embrittlement of Duralumin III - Effect of the Previous Treatment of Sheet Metal on the Susceptibility to this Type of Corrosion

Light aluminum alloys of the duralumin type, that is, high—
strength wrought alloys wEose properties can be iEproved deciId—
edly by heat treatEent are of very IgreaE iEportancei especially
in the form of sheeE Iand tubes, for aircraft Iconstruction. The
permanence of such_ materials Iwhen exposed to corrosive condi—
tions such asI anI obEainI in aircraft service should be known
however, _witE Ia highI degree IoIf certalnuy and precautionary meas—
ures takenI tIo guard against any possible serious deterioraticnil
in service.

The obedient reliable information along this line aE
Iinvestigation, the reIsultsI oIf which rorm the basis Iof this series
of_ reports (Reference Il).,I hIas been carried out at the Bureau of
Standards in Icooperation with the National AdvisoryI Committee -
for Aeronautics, Bureau of Aeronautics of the Navy Department,
and ArmyI Air Corps.- The leading manufacturers have also partic—
ipated in the investigation by furnishing practically all of the
materialsIneeded. The investigation, which was started in the
latter part of 1985, is still in progress and final and complete
answers have not been reached on all points concerning the permar-
nence of duralumin in service. The information which has been
obtained, however, is of very considerable Value to both manu—
facturers and users of—aircraft and its_publication at this time
would seem to be warranted'althbugh-pcssibly some of the state—
ments made may be modified slightly in the light of future re—
sults.

In the preceding report of this series, the deteriorating
effect of intercrystalline corrosion upon the tensile proper—
ties of sheet duralumin was described and it was shown by means
of accelerated corrosion tests that the duralumin type of alloy
is, in general, subject to this form of deterioration. Although ,
some of the different heat—treatable aluminum alloys are much
more susceptible to the intercrystalline form of corrosion than
others, the cemposition of the alloy does not appear to be the
single controlling factor. Brief reference was alsp made to
the fact that duralumin obtained from different sources frequent—
ly varied very considerably in susceptibility to intercrystalline
corrosion. Mention was also‘made to the effect that, with the
same material, the corrosion resistance appeared to vary accord—
ing to its previous treatment, particularly its heat treatment.
The outstanding characteristic of duralumin and the one which
underlies its usefulness as a high—strength light alloy, is
the fact that its mechanical properties can be very materially
improved by heat treatment.