A Caltech Library Service

Age Hardening of Heat Treated Aluminum Alloy. An Investigation of the Fluctuation of Hardness with Time of Ageing of Heat Treated Aluminum Alloy Sheet


Moore, Charles Kenneth and Nollan, John Lloyd (1937) Age Hardening of Heat Treated Aluminum Alloy. An Investigation of the Fluctuation of Hardness with Time of Ageing of Heat Treated Aluminum Alloy Sheet. Master's thesis, California Institute of Technology. doi:10.7907/3G1Z-F889.


The authors have found what they believe to be a tendency for a certain Aluminum Alloy, namely 24-SO, to fluctuate in strength, and hardness, during the process of age hardening, after heat treatment.

This variation in hardness of the material, while the ageing process is going on, is accompanied by a change in ultimate strength, and in the stress-strain relationship of the material; and in general the condition of the alloy is indicated by the hardness number.

The limited scope of this research does not indicate that this phenomenon of fluctuation of hardening is constant in occurrence; as the number of tests made were insufficient to determine the regularity, or irregularity, of this characteristic of the material.

All of the metal tested became stable within the commonly accepted range of ultimate strength for this alloy.

From these few experiments it appears that although the hardness varies with time, the alloy, if allowed to age sufficiently, will develop its rated strength.

Various reports have been made to the effect that sheet aluminum alloy, after being heat treated, quenched, and allowed to begin normal age hardening, did not respond to ageing as might be expected, nor did it follow the theoretical hardening curve with reasonable agreement. It was found that sheet material, although apparently properly heat treated, had not hardened, or acquired its full strength, when inspected by hardness testing methods.

From observations it was found that the same piece, which was observed to be soft, when allowed to age for a longer period and tested again for hardness, had in some cases come up to the required standard, and in others had exceeded the inspection limits.

To the best of the authors knowledge no systematic investigation of this phenomenon has been undertaken, and as a preliminary quest in this field of research a periodic measurement of hardness, and tensile strength, was carried out to determine the actual manner in which the selected material would harden with time, and to correlate its indicated hardness with the strength of the piece at the time of measurement.

Item Type:Thesis (Master's thesis)
Subject Keywords:Aeronautical Engineering ; Mechanical Engineering
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Mechanical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Sechler, Ernest Edwin (advisor)
  • von Kármán, Theodore (advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 January 1937
Additional Information:Charles Moore received his Masters degree in Aeronautical Engineering. John Nollan received his Masters degree in Mechanical Engineering
Record Number:CaltechETD:etd-03212005-103521
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1039
Deposited By: Imported from ETD-db
Deposited On:21 Mar 2005
Last Modified:16 Feb 2023 18:51

Thesis Files

PDF (Moore_ck_1937.pdf) - Final Version
See Usage Policy.


Repository Staff Only: item control page