Search

The annealing property of A1050 sheet is strongly influenced by the intermediate annealing (I. Ann.) condition, especially by the heating rate and annealing temperature. Rapid heating and high temperature annealing will retard the recovery at final annealing (F. Ann.). This is the reason why the CAL (continuous annealing line) I. Ann. is superior to conventional batch type I. Ann. in resistance to softening by F. Ann. Specific resistivity measurements and chemical analyses of extracted intermetallic compounds showed that the softening behavior depends on the iron concentration in solid solution (CsFe) and that the CsFe after I. Ann. is a function of that before I. Ann., heating rate and I. Ann. temperature. The CsFe before I. Ann. will be kept almost constant on reaching the annealing temperature in case of rapid heating (salt bath). On the contrary, it will be decreased by precipitation during slow heating and re-solution will take place at temperature above 400°C in case of slow heating (20°C/Hr). Yield strength after F. Ann. (220°C × 5Hrs.) showed good corelationship with caluculated CsFe after I. Ann.

The relationship between the cast structure of commercially pure aluminum ingots and the intermetallic compounds were studied by using an E. P. M. A., a scanning electron microscope, an X-ray diffractometer and a Mossbauer effect spectrometer. The intermetallic compounds were extracted out of several regions of A1100 ingots made by semi-continuous casting with the method reported previously. The size of the intermetallic compounds was found within the range of 0.8μ and 50μ. The intermetallic compounds in the inner region of the "Fir tree" structure were mainly Al6Fe, while outside this region the intermetallic compounds were mostly Al3Fe. However, besides these two major compounds, the unknown compound, which presumably corresponded to the Al-Si-Fe phase, was also found.

Experiments have been made to examine the effects of cold working on the rate of cluster formation and precipitation in Al-4%Cu or Al-1.8% Cu alloys with X-ray Laue Photographs, electron micrographs and measurements of micro-hardness. The correlation between cold woring and the excess vacancies retained in quenching was investigated with water quenched, air cooled and reverted specimens. The effects of cold working after aging at low temperature were also examined here.The experiments provided evidence that the formation of the less stable G. P. (1) and G. P.(2) is hindered, while the precipitation of the more stable θ' phase is accelerated.The rate of precipitationis more rapid in water quenched specimens than in air cooled, or reverted materials. The increased rate is due to the fact that the lattice vacancies which are more than the equilibrium are retained in quenching. The suppressive effects of cold working are most remarkable in water quenched alloys.The mechanism by which the rate of cluster formation is retarded may be due to two effects: one is the sweeping out of the quenched-in vacancies, which are necessary for solute diffusion, by the motion of jogs in dislocations during plastic deformation or the increase in the rate of annealing of quenched-in vacancies as a result of cold working; and the other is the formation of many smaller enriched clusters of solute atoms which are formed by the stronger binding interaction between solute atoms and lattice defects introduced by cold working.

Aluminum alloys, containing larger amounts of manganese above the maximum equilibrium solubility, were solidified by cooling the molten alloys in a special copper mould. The structures and properties of the solidified alloys and their decomposition process by annealing at various temperatures were examined by means of optical and transmission electron microscopes, X-ray diffraction analysis, microhardness test, and electric resistivity measurement.The results obtained were summarized as follows.(1) Solid solution containing a considerably large amount of Mn was easily obtained with aluminum alloys. The degree of supersaturation depended upon the cooling rate from molten state. The structure was not completely homogeneous; i.e., the solute concentration on the cell boundaries was higher than that in the interior of the cell. The difference in the above concentrations was greater with higher content of Mn or lower cooling rate.(2) Discontinuous precipitation was observed on the cell structure when annealed at some temperatures. When annealed at above 550°C, Al6Mn was found to be as a stable second phase and it was replaced by G phase at annealing temperatures below 550°C. The G phase was more easily formed when the degree of supersaturation was relatively low.