Page 10 - Jan-Feb 2018
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Technology
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Directorate of Naval Architecture         Fin Stabilised Armour                     component is made of this alloy for
(DNA), Integrated Headquarters,           Piercing Discarding                       Mk-II FSAPDS ammunition. For Mk-
MoD (Navy) in September, 2014.            Sabot (FSAPDS): An Anti-                  II FSAPDS ammunition, the tail fin is
Indian Navy, in February, 2016,           tank Ammunition                           made out of steel.
placed bulk order on BALCO for the
procurement of the aforementioned            DTD5124 is an Aluminium-zinc-             During the course of technology
materials. However, in early 2016, M/s    magnesium-copper based 7xxx series        development, some technical
BALCO took an internal decision to        aluminium alloy, the class of highest     problems faced were:
close the downstream facilities for the   strength aluminium alloy produced         (i)	 An unacceptable percentage
production of hard alloys. As a result,   by the ingot metallurgical route. The     of rejection of the fully heat treated
it became necessary to establish an       chemical composition of DTD 5124          extrusions due to the formation of
alternate source for the production of    alloy (introduced in UK) is similar to    an increased width of the peripheral
alloy DMR291A sheets at Hindalco,         that of alloy AA7075 of Aluminium         recrystallised layer (i.e., as high as
Hirakud, wherein, a 4-high rolling        Company of America (ALCOA), USA.          21 mm for the 116 mm diameter
mill is available to produce these                                                  extrusions)
materials.                                   Aluminium-zinc-magnesium-              (ii)	 Inadequate strength properties
                                          copper based Directorate of Technical     of the DTD5124-T651 extrusions
   As a first step, Hindalco carried out  Development (DTD) UK, 5124 alloy is       for the present application. The
trial production of DMR291A sheets        utilised for the manufacture of tail fin  typical T651 strength properties of
of thicknesses 0.9 mm and 3.5 mm in       and sabot components of FSAPDS, an        this alloy, i.e., 0.2 per cent, PS of 500
H24 temper. The sheets were made          anti-tank ammunition, used by Indian      MPa, UTS of 570 MPa were lower
using the same process schedules          army. Typically, these components are     than the minimum required strength
established earlier by DMRL at            machined from heat treated (T651)         properties of 0.2 per cent, PS of 520
M/s BALCO, Korba. The production          DTD5124 round bar extrusions of           MPa and UTS of 580 MPa for the
trials at Hindalco, Hirakud occurred      suitable diameters and hard anodised      81 mm diameter extrusions from
under the supervision of DMRL. The        prior to its use. Hard anodising          which the tail fin component used to
sheets were acceptable in terms of Dye    provides thermal barriers to the          be machined
Penetrant (DP) tests and dimensional,     components during exposure to high        (iii)	 Rapid voltage rise with time
thickness and flatness checks             temperatures for a few milliseconds       during hard anodising of the tail fin
carried out at the site by a team of      during firing, and also protects the      and sabot components made from
representatives from DNA, DQA(N),         material against general corrosion        the indigenised DTD 5124-T651
QAE(N) and DMRL. Other tests, i.e.,       during long term storage.                 extrusions. As a result, the process
corrosion and weldability, as a part of                                             had to be interrupted to avoid burning
the acceptance tests were also carried       While both, tail fin and sabot         of the components
out at CECRI and WRI, respectively.       are made of DTD5124 for Mk-I
Based on these results, the Indian        FSAPDS ammunition, only the sabot
Navy has decided to place bulk orders
on Hindalco for the procurement of
the DMR291A sheets.

(a) Sabot and (b) Tail fin, both machined from indigenised DTD5124-T651 extrusions, and
           (c) hard anodised tail fin, and (d) a couple of hard anodised sabot petals

10 January-February 2018                  Aluminium Alloy Technologies for Advanced Defence Systems
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