Page 8 - Jan-Feb 2018
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utilised in SLBM-K4 flight trial held    working schedule was earlier utilised      M/s Siddhi Engineers, Ahmedabad
in 2014. Several of these indigenised    to produce Alclad AA2219-T87            (who successfully produced the thin
components were further successfully     plates at BALCO for BrahMos missile     walled tubes of alloy BAPL5xxx for
utilised in successive flight trials.    applications.                           BrahMos missile earlier using billets
                                                                                 from HAAL and mother hollow
   The nose cap dome components          Akash Missile                           tubes from OFAJ) produced the
were made from 30 mm thick                                                       AA6082 straight tubes for Akash.
AA2219-O (annealed) plates, and             Akash, a medium-range surface-to-    DMRL provided crucial metallurgical
later heat treated to the precipitation  air missile, currently being produced   inputs in terms of optimum alloy
hardening temper. One such               for Air Force and Army is a ramjet      composition, ingot quality check
component was successfully utilised      propelled missile with air intakes      procedures and billet acceptance
in SLBM-K4 flight trial held in 2017.    manufactured from aluminium alloy       criteria to the firm to procure billets
These nose cap domes will continually    AA6082 seamless tube. This tube is      and the resultant mother hollow tubes
be used in all future SLBM-K4 flight     imported from various sources abroad    of 122 mm OD and wall thickness
trials.                                  as a straight tube of 114 mm OD, wall   varying from 5 mm to 8 mm. Further
                                         thickness of two mm and length as       inputs, in terms of formulation of
   Yet another component, i.e.,          1500 mm. The tube is then bent as       process schedules for the manufacture
alignment cylinder, made from            per the design requirement and heat
20 mm thick AA2219-T87 plates, shall     treated to the peak aged temper for                                 AA6061-T6
be used in the future flight trials of   the actual application.                                             t = 2.4 mm
SLBM-K4 missile.
                                            Indigenised AA6082-O straight tubes          Indigenised AA6061-T6 sheet
   The temper T87 implies the
provision of a minimum of seven                                                           Indigenised AA6061-O sheet
per cent (and not exceeding 8 %) cold
work by stretching prior to artificial
aging. However, the capacity of the
stretching machine at BALCO, Korba
was not sufficient to impart seven
per cent stretching to these wide and
thick plates.

   Using the rolling mill and 250 T
stretching machine available at DMRL,
it was formulated that a combination
of pre-aging cold work involving
five per cent cold rolling followed by
two per cent stretching (i.e., a total
of a minimum of 7 % cold work)
imparts desired strength properties
in T87 temper. In fact, the same cold

                                                                                 Boat tail

               Indigenised tube, bent as per the design  Boat tail component (arrowed) in NGARM, fabricated from
                                                                             indigenous AA6061-O sheets
8 January-February 2018
                                                            Aluminium Alloy Technologies for Advanced Defence Systems
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