ON THE GERMINATION OF THE ANNEALED ALUMINUM SHEET WHICH IS CONTAINED MANGANESE AS THE IMPURITY AND ON THE ALLOWABLE LIMIT FOR THE CONTENT OF MANGANESE

Abstract

When the small amount of manganese are contained in the commercially pure aluminum, the remarkable grain growth and the germination by deep drawing sometimes take place in the annealed sheets.In this paper, we intended to determine the allowable limit of manganese content up to which the grain growth and the germination are not caused under the normal annealing condition of commercially pure aluminum.The results obtained are as follows.(1) When the manganese content is not more than 0.05%, any annealing methods may give the successful results.(2) Although the manganese content increases over 0.05%, the high temperature-short time annealing above 500°C. is proved satisfactory up to 0.10%Mn.(3) In the range of low manganese content, too high annealing temperature is not preferrable, but in the high manganese content range close to 3S, it is indispensable to anneal in the high temperature salt bath.(4) Although the effect of heating rate is very remarkable, this heating rate is not so low speed order that has been considered to date, but it is so higher speed order as the difference between air bath heating and salt bath heating. Moreover, it seems to be the heating rate at which the specimens pass through some considerablly lower range (probably close to starting temperature of recrystallization) that affects the size of recrystallized grain.(5) There are two temperature ranges which have the relation to the growth of recrystallized grain. One is in the relatively lower range of temperature, and the other is in the higher temperature range. The former is probably based on the production of recrystallized nucleus and the latter seems to be based on the secondary growth of recrystallized grain. In the lower manganese content range, the effect of latter may be stronger, but as manganese content increase, the effect of former may be rather more remarkable.(6) Although it has been belived that the germination has a relation to the recrystallized grain size, there seems to be no relation in the low manganese content range where the grain size is 0.05-0.1m/m The erichsen value of annealed sheet has not any relation to their germination which presented on the surface of the testing cup.