Page 11 - Jan-Feb 2018
P. 11

                                                                                                             FocusVVSDSDuu¨¨yykkWtWthh QQ¨¨ddll

   The use of zirconium additions                                  Inhibition of growth of the anodic oxide
together with reductions in the initial                              coating by Al12(FeMn)3Si particles
billet temperature and the ram speed
restricted the width of the peripheral                                     A uniform growth of the anodic         (a) DP test carried out on a hinge
recrystallised layer to ≤1.5 mm                                        oxide coating in the absence of the      component of alloy RDE40 revealing
on peak aged extrusions of all the                                                                              presence of cracks, and (b) Presence
three sizes (i.e., 81 mm 116 mm and                                            Al12(FeMn)3Si particles          of cracks in regions away from hinge
135 mm). The conventional single                                                                                  locations, as detected by DP tests
step artificial aging was replaced                                 DTD5124-T651 extrusions, were
by a suitable two-step artificial                                  successfully test fired.                  have been used for rocket nozzles,
aging treatment. This aging practice                                                                         mandrels for propellant casting,
improved the peak aged tensile                                     Other Ammunitions                         electronic housings and several
properties of all the three sizes of                                                                         other components for a variety of
the extrusions. The two-step aging                                    Aluminium–magnesium–silicon            ammunitions.
treatment is based on the concept that                             based alloy AA6082 was produced
the formation of strengthening phases                              in the form of extruded rods (having      Sarvatra Bridging
during artificial aging treatment (at                              three different diameters, i.e., 60 mm,   System
relatively higher temperature) could                               100 mm and 150 mm) and heat treated
be aided by prior formation of solute                              to T651 temper at OFAJ, Nagpur,              7xxx series aluminium alloys are
clusters/Guinier-Preston zones by                                  under a DRDO project. This alloy has      based on aluminium-zinc–magnesium
the use of a suitable low temperature                              a combination of good strength and        and aluminium–zinc–magnesium–
artificial aging (i.e., this temperature                           corrosion resistance. These materials     copper systems. The copper-bearing
being lower than the second step                                                                             aluminium–zinc–magnesium system
artificial aging temperature).                                                                               represents the class of highest strength

Detailed studies carried out at
DMRL showed that the constituent
particles based on   thAel1h2(aFredManno)3dSiisidnog
not dissolve during
treatment, and they inhibit nucleation
and growth of oxide coatings in
local regions, thereby disrupting the
continuity of the anodic coatings.
Further, such particles add resistance
to the electrical path, causing a rapid
rise in the bath voltage with time, often
causing burning of the components.

It was established that in the absence
otyfptehseoAf tlh12e(FFeeM-bne)a3rSiinpghpahsaes,etshfeoromtheedr
in the alloy do not survive the hard
anodising treatment. This results in a
steady rise in bath voltage with time
and a uniform growth of the anodic
oxide film. Reductions in Fe, Si and
Mn impurities below certain levels in
the alloy inhibited the formation of
the  Aplr1o2(vFiedMedn)a3Ssiopluhtaiosen  in  the  alloy,
and                                       to  the  hard
anodising problem.

   The FSAPDS ammunitions of                                       Indigenised AA6082-T651 extrusions produced at OFAJ, Nagpur
different calibres fitted with tail fin and
sabot, fabricated from the indigenised

Aluminium Alloy Technologies for Advanced Defence Systems          	 January-February 2018 11
   6   7   8   9   10   11   12   13   14   15   16