Effects of iron and Silicon on Recrystallization Textures of Drawn Aluminium

The recrystallization textures of cold drawn aluminium alloys 
were determined by means of the orientation distribution functions 
(ODFs). The changes in texture with annealing temperature were 
interpreted by examining the interrelation between recrystallization 
and precipitation. The drawing textures of all the specimens 
are mainly composed of the fiber component. In the case of 
Al-Si, silicon exists in the solid solution at high and medium 
temperatures (623-723K), therefore, the component is 
sharpened and the recrystallization textures are composed of the 
strong component and the weak one. On the other hand, 
precipitation of silicon participates in recovery and recrystallization 
at low temperatures (523-573K) so that the component 
nearly equals to the one in intensity. Al-Fe shows the 
strong + weak fiber texture in the all ranges of 
annealing temperatures, though the component is stronger at 
a high temperature (723K), where precipitation occurs after 
recrystallization, than at low and medium temperatures (573-673K), 
where it does before recrystallization. For Al-Fe-Si, the recrystallization 
textures are almost the same as Al-Fe except for 
weakening in orientation density.


INTRODUCTION
It is known that the recrystallization textures of aluminium alloys are varied with annealing temp.erature particularly, in case of precipitating during annealing :t). The recrystallization texture of cold rolled aluminium usually consists mainly of the cube orientation. However, R-texture which is similar to the rolling texture is formed when the precipitation occurs during the recrystallization, because the fine particles of precipitates hinder the motion of the sub-boundaries and the dislocations 2).
In this study, the recrystallization textures at various annealing temperatures were measured in drawn aluminium containing a slight amount of iron and silicon and then an understanding of changes in fiber textures was acquired by clarifying the relation between recrystallization and precipitation.

EXPERIMENTAL PROCEDURE
Five kinds of specimens, 99.9wt%Al, AI-0.05%Fe, AI-0.26%Fe, AI-0.1 l%Si and Al-0.27%Fe-0.11%Si, drawn to 90% reduction in area were isothermally annealed at 573K, 623K, 673K, 723K (in addition, 523K for AI-0.11%Si) in a salt bath. The process of recrystallization was investigated by means of the hardness measurements and the optical microscopic observations. The beginning of precipitation was determined by means of the electrical resistivity measurements. In addition, an electron microscope was used in order to observe both the microstructures and the precipitates. The texture measurements in the central region of specimens were carried out by the X-ray diffraction method. {111}, {200} and (220} pole figures were measured from which the three-dimensional orientation distribution functions (ODFs) were calculated by the series expansion method of BungCs. Furthermore, the inverse pole figures were made from ODF data. EXPERIMENTAL RESULTS AND DISCUSSION Figure 1 shows the variation of electrical resistivity with the isothermal annealing. In the case of AI-Si alloy, the electrical resistivity decreases gradually with the annealing temperature below 573K, While increases above 673K. It was found that the increasing of the electrical resistivity was due to resolution of silicon which was once precipitated by annealing or existed in the matrix before annealing, because the amount of precipitated silicon decreased from 0.018wt% to 0.002wt% with the annealing for 20s at 673K.
In the case of AI-Fe and AI-Fe-Si alloys, the electrical resistivity decreases in the all ranges of annealing temperatures but slightly at higher temperatures, because the solubility limit of Fe in Al is enlarged at higher temperatures.
Fiber texture in the drawn state consists mainly of the < 111> orientation component in all specimens 3)'4), and the weak <100> one is also found in 99.9%A1 and Al-0.27%Fe-0.11%Si. In all specimens, the 111/100 fiber texture is observed after the annealing. However, the fraction of the 100 component to the 111 one depends on both the alloying elements and the annealing temperature. The dependence of annealing temperature on recrystallization texture is roughly divided into two types.
Anneol Ing Ime I s      (Fig.5(a)), the recrystallization occurs independently on the precipitation at high and medium temperatures. Therefore, the 111 fiber-texture component recovers and recrystallizes more preferentially than the 100 one since the recrystallization is not suppressed by precipitation. Furthermore, it is supposed that the crystals with the near 111 orientation rotate toward the stable l I 1 one with the help of thermal activation. In the case of lower temperature, the precipitation occurs during the process of recovery or recrystallization. Therefore, it is considered that the 100 component which is usually found in the recrystallization texture of aluminium increases, since the recovery and growth of the 111 oriented sub-grains are suppressed due to hindering the migrating sub-boundaries by fine precipitates. But there is a difference between 99.9%A1 and AI-0.11%Si. In the case of 99.9%A1, the precipitation does not occur even at lower temperature and hence the 111 component remains strongly in comparison with Al-0.11%Si. For AI-0.26%Fe (Fig.5(b)) and AI-0.05%Fe, as well as A1-0.1 l%Si, at low and medium temperatures, the precipitation occurs in the process of recovery (or the early stage of recrystallization), so that the <111> fiber-texture component becomes weaker than that at a high temperature where precipitation occurs after the recrystallization. Though the 111 component, in Al-0.26%Fe, is stronger than the 100 one at all ranges of temperatures. For Al-0.27%Fe-0.11%Si (Fig.5(c)), the precipitation occurs preferentially at all ranges of annealing temperatures. Therefore the 111 fiber texture component becomes rapidly weaker than the 100 one, and the 100 component is stronger than the 111 one at low and medium temperatures. From the consideration of the transmission electron micrographs and selected area diffraction patterns of AI-Fe annealed at 573K for 700s, it was recognized that the matrix was composed of two regions, that is, the 100 and the 111 components parallel to the drawing direction. The 100 component region was composed of the microband accompanied with the large sub-grains, while the 111 component region was surrounded by the small sub-grains. The matter mentioned above will interpret that the rate of recovery and grain growth in the 100> region is faster than that in the 111> region 5)-7). CONCLUSION Compared with the deformed state, the lll fiber-texture component increases or remains strongly in the case of higher temperature annealing. In the case of lower temperature, the 100 one increases and 111 one decreases. But the 111 one is further reduced if the precipitation occurs during the process of recovery or recrystallization. It is supposed that this may be attributed to the pinning effect by fine precipitates.