Source of information: Division of Materials Science and Engineering, Korea University, Seoul 136-701, Republic of Korea
The effect of lubrication on the evolution of microstructure and texture during hot rolling was studied by means of texture analysis and ?nite
element method (FEM) simulations. Hot rolling with lubrication gave rise to the formation of uniform rolling texture in the whole thickness layers,
whereas hot rolling without lubrication led to the evolution of the pronounced through-thickness texture gradients. FEM calculations reveal that a
larger friction between roll and sample causes a strain state severely deviated from a plane strain leading to the formation of shear textures in the
thickness layers close to the surface
Rolling deformation can be simpli?ed by a plane strain state.
However, the strain state during rolling is strongly deviated from
a plane strain state, since factors like geometrical changes during
a rolling pass, friction between roll and sheet surface and strain
and temperature gradients upon hot rolling can cause severe
deviations from the plane strain condition (e.g. [1,2]). Besides,
these parameters depend on the thickness layers of the rolled
sheet, which results in different strain states leading to different
rolling textures at different through-thickness layers of the sheet.
The evolution of through-thickness texture gradients during
cold rolling was reported in detail elsewhere (e.g. [3–5]). How-
ever, studies during hot rolling of aluminum sheets are rather
limited so far. The present work aims to yield experimental
results on cause and formationmechanisms of through-thickness
texture gradients in hot rolled aluminum sheets, which were
deformed by hot rolling with and without lubrication. The effect
of the different local strain states through the sheet thickness
on the microstructure and texture during hot rolling was stud-
ied by X-ray macro-texture analysis and EBSD micro-texture
measurements. In order to interpret the variation of strain states
in a roll gap, the ?nite element method (FEM) simulation was
performed by varying the frictional condition between rolls and
rolled samples.
The as received material was hot band of the commercial aluminum alloy AA 1050 with a thickness of 10mm. The center layer of the hot band displayed the partially recrystallized microstructure, while fully recrystallized grains were observed at the sheet surface. In order to produce the texture and microstructure more homogenously, the hot band was annealed at 450 ?C for 10 h, which pro- vides equiaxied grains of 60m in diameter with a fairly random texture. This initial sample was heated to 350 ?C and hot rolled using a laboratory rolling mill with a roll diameter of 118mm in one pass to 6.0mm, corresponding to a thickness reduction of 40%. To obtain different strain states through the sheet thickness, one sheet was rolled dry, i.e. without using a lubricant, and these specimens are hereafter denotedWOL (‘without lubrication’). Other specimens were rolled by applying a lubricant, these specimens are referred to asWL (‘with lubrication’).
The crystallographic textures of the rolled sheets were determined by mea- suring pole ?gures by means of an X-ray texture goniometer. From three incomplete pole ?gures, the orientation distribution functions (ODF) f(g) were calculated [6]. To determine the texture variation through the thickness, X-ray texture measurements were performed at four different layers of each speci- men. In this paper, the layer analyzed is characterized by the parameter s, and s = 0.0, 0.5, 0.7 and 1.0, respectively, denote the center layer, the mid-thickness layer between center and surface, a layer close to the surface and the sam- ple surface. The micro-texture was analyzed through electron back-scattered diffraction (EBSD) [6]. The measurements were carried out in a scanning elec- tron microscope (SEM) equipped with an EBSD detector. EBSD measurements were performed in the longitudinal section (i.e. from the TD).