Microstructure Evolution Of Aluminum Research Articles

Microstructural evolution of aluminium in dissimilar A1050/S45C FSW joints by Zn interlayer

This study investigated the microstructural evolution of A1050 stir zones in dissimilar A1050/S45C friction stir-welded joints fabricated with 100- and 200-µm-thick Zn interlayers in addition to a third joint without any interlayer. The dissolved Zn in the A1050 stir zones contributed to its strengthening by forming Al–Zn solid solution. The addition of Zn refined the A1050 grains with many well-defined high-angle grain boundaries. The effect of Zn in the A1050 strengthening and grain refinement becomes apparent with a relatively high content of Zn. The possible precipitation of Zn-rich particles along the A1050 grain boundaries may also contribute to the A1050 stir zone strengthening by retarding the dislocation motion and enhancing the discontinuous dynamic recrystallisation.

Comprehensive understanding of the mechanical properties and microstructure evolution of aluminum alloy/steel laminates during friction stir-assisted incremental forming with synchronous bonding process

Aluminum alloy/steel laminated parts can be fabricated by separated sheets based on a friction stir-assisted incremental sheet forming with synchronous bonding (FS-ISF&SB) method. The current work aims to realize comprehensive understanding of microstructure evolution during FS-ISF&SB and its effect on mechanical properties of the formed parts. Three typical sets of experiments with different combinations of process parameters are carried out, and three different regions are classified by grain feature, defined as deformed region, loading region and undeformed region. Recrystallization and recovery behaviors occur at all of the three regions on both sheets, which generate softening effect. However, the effect of work hardening keeps a dominant role on mechanical property compared with softening effect on steel, while the influence level of these effects on aluminum alloy is opposite during FS-ISF&SB. Besides, stratified structure and gradient distribution of grain size from the outer surfaces to the interface are observed. The microstructure evolutions greatly accelerate the atomic diffusion and subsequently promote the metallurgical bonding of the laminates. It is also found that Fe–Al intermetallic compounds (IMCs) consisting of FeAl3 and Fe2Al5 are generated on the dissimilar interface of the fabricated parts. The thickest IMCs are usually found at the loading regions. Moreover, the maximum nominal bonding stress obtained by peeling test of the laminated parts can reach 100.0 MPa with the moderate thickness of IMCs as of 13.1 μm.

Microstructure Evolution of Aluminum Deformed by Combination of KoBo Extrusion and Differential Speed Rolling (DSR)

In the present paper results of a microstructure examination of aluminum deformed by a two step process composed of a combination of two continuous straining methods – the KoBo extrusion and a cold rolling have been shown. The cold rolling was conducted in two variants – with an equal speed of both rolls (ESR) and with a differentiation of the upper ad the lower roll speed (a differential speed rolling – DSR). Results of a transmission electron microscopy (TEM) analysis revealed that applied processing strongly affects a microstructure of the examined material. It is shown that selected parameters of the KoBo extrusion allow obtaining a fine grained material with a grain size in the range of 1÷3 μm. Since a subsequent deformation of as KoBo extruded aluminum bars through the conventional rolling (ESR) leads to a formation of normally observed structural features (e.g. deformation bands), an application of the DSR methods results with a further grain refinement effect. It is found that, the KoBo extrusion combined with the DSR deformation allows obtaining aluminum plates that are characterized by a homogeneous structure with the grain size in the submicron range.

Microstructural evolution of aluminium–copper alloys during the downward directional solidification process

Abstract The microstructural evolution of Al–Cu alloys during the downward directional solidification process was investigated. At the planar-to-cellular transformation point, the planar liquid/solid (L/S) interface broke down at the centre. This was contrasted with the behaviour in the liquid metal cooling process, where the interface broke down at the periphery. The critical withdrawal rate at this point was higher than the theoretical value. In addition to this, the variation in the primary dendrite arm spacing (λ 1) as a function of the withdrawal rate (V) at constant G L for the Al-2.0 wt.% Cu alloy agreed with the conventional processes. The comparison of λ 1 in our experiment to the calculated value λ 1 using the Kurz–Fisher, Ma and Trivedi models showed that λ 1, calculated by these models, overvalued our experimental results. However, the λ 1 calculated from the Hunt model agreed well with the experimental values of λ 1. When we reduced the diameter of the sample from 13 mm to 9 mm and maintained the other parameters constant, the L/S interface retained a planar shape. This indicated that the L/S interface was more stable in the smaller sample than that in the larger. This result contrasted with the result in the liquid metal cooling process.

Spontaneous Crystalline Multilayer Formation in Ni Implanted Al at 100 K

AbstractThe microstructure evolution of aluminum implanted with nickel at 5 MeV and at 100 K to a local concentration of 25 at. % is described. Transmission Electron Microscopy (TEM) observa- tions and Rutherford Backscattering Spectrometry (RBS) experiments are conducted to deter-mine the Ni profile and the microstructure of the implanted samples. For lower Ni concentration, it has been previously observed that Al0.75Ni0.25 amorphous precipitates are formed together with a high dislocation density. When the Ni concentration reaches 25 at. %, a new crystalline multi-layered microstructure is observed: the TEM observations reveal the presence of well-defined crystalline layers separated by sharp interfaces. To our knowledge, it is the first time that such a structure is observed without further annealing of the implanted sample. A series of mechanisms describing the formation of the crystalline multilayer are briefly discussed. It is argued that its formation is the result of a recrystallization front produced by the exothermal amorphous to crystal transformation.