The Use of Novel Processing Procedures for Improving Overall Fatigue Resistance of High Strength Aluminum Alloys.
Annual rept. 1 Jan-31 Dec 85,
VIRGINIA UNIV CHARLOTTESVILLE DEPT OF MATERIALS SCIENCE
Pagination or Media Count:
Its objective is to develop an understanding of the mechanisms involved in the initiation and propagation of cracks in metals in order to optimize the microstructure of high strength aluminum alloys for overall fracture resistance. The research conducted during this year was divided into three tasks. Task I was concerned with the effects of slip character and grain size on the intrinsic material and extrinsic closure contributions to fatigue crack growth resistance of 7475. It involved the use of thermomechanical processing to modify the grain structure for enhancement of both intrinsic and extrinsic effects. In our last report we described the use of a direct current potential drop technique DC-PD to examine the possibility of crack tip welding in vacuum and the results of our initial experiments using this method. Task II was concerned with a study of the fatigue crack growth and fracture mechanisms of an Al-Li-Cu alloy. Task III was concerned with secondary cracking in Al-Li-Cu, Al-Li-Mg and Al-Li-Cu-Mg alloys. Many recent studies of this class of alloys have shown that they can exhibit severe grain boundary cracking. The most commonly-observed manifestation of this cracking is the appearance of secondary cracks on fracture surfaces of tensile specimens loaded parallel to the rolling direction.
- Metallurgy and Metallography