Toshiya Shibayanagi

Effect of friction stir processing tool probe on fabrication of SiC particle reinforced composite on aluminium surface

Abstract An investigation has been carried out of the effects of tool probe shape and size on the formation of surface composite by uniformly distributing SiC particles into a surface layer of an A1050-H24 aluminium plate through friction stir processing (FSP). Tool probes of three different diameters (3, 5 and 7 mm) and four different shapes (circular with threads, circular without threads, square and triangular) have been used to fabricate the surface layers at rotation speeds of 1500–2250 rev min−1 and a travelling speed of 1·66 mm s−1. The SiC particles were packed into a groove of 3 mm width and 1·5 mm depth cut on the aluminium plate and covered by an aluminium sheet of 2 mm thickness. A rotating tool was plunged into the plate through the cover sheet so that the tip of the probe reached beyond the bottom of the groove. As a result, it was found that the square probe dispersed the SiC particles homogeneously in the nugget zone compared with other probe shapes regardless of the rotation speeds. Furthermore, the distributed particles and also the aluminium matrix grain size became finer by the use of square probe than those of the other shapes. On the other hand, the wear rates of the square and triangular probes were higher than that of circular shape. The worn iron debris from the tool reacted with aluminium matrix and form fine iron aluminides compound dispersed in the nugget zone. The probe size had limited effects on the homogeneity of the SiC particles distribution in the nugget zone; the distribution of SiC particles obtained by triple FSP passes was less homogeneous when the probe size was smaller. Microhardness of the nugget zone was homogeneously increased to a level as high as 60 HV with tool of square probe shape after three passes to be compared with 23 HV of the aluminium matrix beside the nugget zone.

Fabrication of in situ Al2O3/Al composite via remelting

Abstract In the present work, in situ Al 2 O 3 /Al composite was produced via CuO/Al composite and subsequent remelting, and the chemical reaction evolution and the fractography were investigated by means of differential scanning calorimeter (DSC), X-ray diffraction (XRD), electron probe micro-analysis (EPMA) and scanning electron microscopy (SEM). The experimental results showed that Al 2 O 3 could be successfully formed in situ by the addition of CuO to aluminum. The results also suggested that the fracture mechanism changed from interfacial debonding in copper oxide/Al composite to particle cracking in Al 2 O 3 /Al composite, which was largely attributed to interfacial bonding increased between in situ Al 2 O 3 particle and Al. The Cu–O stability in the present processing was also discussed from the point view of thermodynamics.

On the role of grain boundary character distribution in grain growth of AlMg alloys

Abstract Grain growth behaviour of recrystallized Al Mg alloys containing 0.3 and 2.7mass%Mg was investigated, focusing on the interconnection between development of the texture and grain boundary character distribution. An Al 0.3mass%Mg alloy showed two stages in the change of microstructure during grain growth: the frequency of cube oriented grains and the ∑1 boundary significantly increased at an early stage and then decreased. In the second stage a small amount of isolated large grains with the non-cube component grew and consumed the surrounding cube grains. In contrast, the frequency of cube oriented grains and the grain boundary character distribution showed no significant change during grain growth of Al 2.7mass%Mg. Small clusters composed of several cube grains containing ∑1 boundaries were formed and their spatial distribution played an important role in the change of microstructure during grain growth. The effect of the spatial distribution on the grain growth behaviour was discussed considering the energy balance at triple junctions of grain boundaries.

Liquid film formation and cracking during friction stir welding

Abstract The influence of tool rotation speed and travel speed during friction stir welding is studied in the case of Al 2024 which contains low melting point phases. When a tool rotation speed of 1600 rev min−1 is applied with a travel speed of 100 mm min−1, S-phase (Al2CuMg) particles in the base material form melted films, promoting the formation of spalling defects comprising subsurface cracks along the trailing edge of the weld below the tool shoulder. Decreasing the tool rotation speed to 400 rev min−1 prevented formation of the melted films by reducing the peak temperature in the stir zone, and avoided formation of spalling defects. When the travel speed is decreased to 32 mm min−1 when using 1600 rev min−1, dissolution of the S-phase occurs and fewer melted films remain in the stir zone. This implies that travel speeds are limited in alloys which contain low melting point phases since these promote cracking defects.

Crystal Structure of CuSn3Ti5 and Related Phases.

Abstract The crystal structure of the ternary phase CuSn 3 Ti 5 has been investigated. The space group is P63/mcm , a =0.8162(1) nm and c =0.5574(2) nm. The structure may be described either as a ternary Ti 5 Ga 4 -type or as a filled D8 8 –Mn 5 Si 3 type. Isotypical phases are observed in the systems M–Sn–Ti with M=Mn, Fe, Co, Ni, Ag or Au.

Effect of grain size on grain orientations and grain boundary character distribution in recrystallized Al-0.3mass% Mg alloy

Abstract The effect of grain size on grain orientation and GBCD of a recrystallized Al-0.3mass%Mg alloy was studied by X-ray diffraction and the SEM-ECP technique. The following results were obtained. 1. 1. The GBCD showed a complicated grain size dependence. The behavior of the GBCD, particularly the frequency of the ∑1 boundary was closely related to the change of grain orientation during grain growth. The increase of the fraction of cube components gave rise to the high frequency of the ∑1 boundary. 2. 2. The growth behavior of the cube grain group composed of several small grains played an important role in the increase of frequency of the ∑1 boundary. Variation of the GBCD was very sensitive both to the local distribution of grains as well as to the grain orientation distribution.

Grain rotation in Ni3Al

Abstract The effect of pre-strain on grain rotation and GBCD in polycrystalline Ni3Al was investigated and the following conclusions were reached. 1. (1) The frequency of coincidence boundaries does not increase by the grain rotation. 2. (2) Pre-strain enhances the grain rotation but does not affect the frequency of coincidence boundaries.

Control of Grain Size and Texture in Al Alloys Utilizing Friction Stir Processing

The present paper deals with the control of microstructure of friction stir processed aluminum alloys focusing on grain refinement, thermal stability at elevated temperature and texture development in some aluminum alloys such as 5083, 6061 and 7075 commercial aluminum alloys. 3mm thickness plates of 5083, 6061 and 7075 Al alloys were friction stir processed/welded with several rotation speeds and travelling speeds. Optical microscopy revealed the grain refinement in the stirred zone of each alloy and the average grain size decreased with decreasing rotation speed under various travelling speeds. Annealing of the joints brought about abnormal grain growth at temperatures higher than 773K for 5083 alloy. Critical temperature of the abnormal grain growth tended to decrease as the rotation speed decreased for the fixed travelling speed. Dissimilar joining of 5083 Al alloy to 6061 Al alloy also showed abnormal grain growth when annealed at 773K. A peculiar texture development of 7075 Al joint showing (111)//ND-oriented grains existing throughout the nugget was revealed by EBSP analysis.

Grain boundary migration in Fe-3mass%Si alloy bicrystals with twist boundary

Abstract The characteristics of grain boundary migration in Fe-3mass%Si alloy bicrystals with ∑3(011), ∑5(001) and ∑9(011) coincidence twist boundaries and random twist boundaries were examined to obtain an information on the development of {110}(001) (Goss) texture. The bicrystals were annealed at 1223 K for an appropriate time and the grain boundary migration speed was evaluated. The ∑5 001l and ∑9 011l twist boundaries showed higher migration speed than ∑3(011) twist boundaries, and the random twist boundaries migrated faster than other boundaries. The migration speed decreased with increasing annealing time due to an increase in the edge components of the lattice misfits in the migrated boundaries. The grain boundary migration was also sensitive to the deviation angle (∆θ) from the ideal orientation relationship for a coincidence boundary. The increase of ∆θ accelerated the boundary migration. The motion of the grain boundary was influenced by plastic strain. Migration of the ∑9 twist boundary was more suppressed by plastic strain than that of the random boundary. On the basis of characteristics of the grain boundary migration, the effect of inhibitor on the Goss texture was discussed.

Polytypism of SiC and interfacial structure in SiCp/Al composites

In the present work, the polytypism of SiC and the interfacial structure between SiC and Al were investigated using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HREM). It was approved that 15R could be juxtaposed with 6H stacking sequences in the same SiC reinforcement and a structural transformation zone was also observed. The Al4C3 compound can nucleate on SiC at the SiC/Al interface with the growth orientation parallel to the C axis of SiC. Mechanisms for the observed phenomena were also discussed in detail.