Angela L. Moran

Improvements in Strength and Stress Corrosion Cracking Properties in Aluminum Alloy 7075 via Low-Temperature Retrogression and Re-Aging Heat Treatments

Abstract The susceptibility of aluminum alloy 7075 (AA7075 [UNS A97075]) to intergranular stress corrosion cracking (SCC) in the peak strength T6 temper is alleviated through the use of the T73, or over-aged temper, which provides improved SCC resistance with a 10% to 15% strength loss compared to the T6 temper. Previous research has indicated that retrogression and re-aging (RRA) heat treatments reduce the trade-off between T6 strength and T73 SCC resistance. The short-term heat treatment they used, however, limited the applicability of RRA to thin sections of material. The primary goals of this research effort were to determine if lower retrogression temperatures could be used in the RRA process to extend the applicability of this heat treatment to thick section aircraft components and to quantify any observed improvements. Alternate immersion (AI) and double-cantilever beam (DCB) tests were conducted in a 0.6-M sodium chloride (NaCl) solution to evaluate the SCC resistance of various tempers. Improveme...

Developing intelligent control for spray forming processes

A program to implement real-time sensing and control of spray-formed preform conditions is underway at the David Taylor Research Center. The objective of the program is to develop sensor and control technologies that can be used to monitor critical process conditions and modify operational parameters during the spray forming of components. This task has been divided into two phases. The first entails developing sensors and controls to monitor and correct simulated process conditions. In the second phase, the selected sensors and controls will be combined with actuators, thereby integrating research center equipment and enabling the production of nonsymmetric preforms.

Spray Forming Alloy 625 Marine Piping

Near-net-shape manufacturing methods for large-diameter Alloy 625 piping have been evaluated to determine cost advantages and product quality over conventional manufacturing and powder metallurgy technologies. One particular method, Osprey spray forming, has proven itself to be a viable alternative. The sprayformed preforms exhibit uniform, equiaxed microstructures and mechanical properties approaching those of wrought via spray forming possesses mechanical properties surpassing those established by current specifications while the microstructures remain fine and quite uniform after cold rolling. In addition, a cost evaluation indicates sizable potential savings when Alloy 625 is produced by spray forming.

A Comparison Study of Stress Corrosion Crack Growth Rates for AA7XXX Alloys as a Function of Bulk Aqueous Chloride Concentrations

Abstract Alternative aluminum alloys are under consideration for drop-in replacement and refurbishment of corrosion and stress corrosion cracking prone AA7075-T6 (UNS A97075) components on aging military aircraft. An assessment of new materials for refurbishment and replacement of older generation, aging components is necessary for a viable life extension program. A quantitative database of stress corrosion cracking (SCC) properties of old generation materials compared to currently available materials is needed as a guideline/justification for part replacement. This effort evaluates AA7150-T7751 (UNS A97150) and AA7040-T7651 (UNS A97040), both which meet mechanical property requirements and are thought to be superior to AA7075-T6 in terms of corrosion performance. Specifically, stress corrosion crack growth rates for these plate alloys were documented and found to be similar in various bulk aqueous chloride environments and to represent a significant improvement over measured rates for AA7075-T651.

An optical roughness sensor for real-time quality measurement

As part of the intelligent processing efforts of the Spray Forming Technology Group at the David Taylor Research Center, a laser stripe sensor has been implemented to monitor preform characteristics. The preform surface roughness is measured in real time and the correlation to preform quality in terms of porosity levels is assessed. The laser stripe method is not a direct indicator of quality, but it can be used with other sensors and advanced control techniques for control of the spray-forming process.

Spray forming technology for military applications

Over the past five years, the Annapolis Detachment, Carderock Division, Naval Surface Warfare Center (formerly David Taylor Research Center) has established a state- of- the- art spray forming facility for the study and exploitation of this near net shape manufacturing process. Spray forming is a single step gas atomization/deposition process which yields ferrous and nonferrous, near final shape, near fully dense preforms that has proven to be a viable and cost effective alternative to conventional metalworking technology for the production of material preforms with properties surpassing those of their cast and wrought counterparts. Current programs at Carderock Divison Naval Surface Warfare Center are aimed at optimization of the process, certification of the spray formed products and industrialization of the technology.

Fatigue failure of an F/A-18 fin retainer spring

Abstract The Navy’s lead missile integration engineer on the F/A-18 E/F program at Patuxent River Naval Air Station supplied a failed LAU-127A/A AIM-9 fin retainer spring for analysis. The spring is responsible for holding the missile’s fins in place while the missile is in the prone position attached to the plane’s wing. The analysis of the spring was conducted to find the mode and cause of failure.

Approach to modeling the spray-forming process with artificial neural networks

In this study artificial neural networks were used to model the spray forming process. Networks were developed and trained using process parameter and product quality data collected from a series of five spray forming runs. Process parameters of time into run, melt temperature, and gas to metal ratio were used as inputs and the networks were trained to predict the corresponding values of exhaust gas temperature, preform surface roughness, and porosity in the product. These networks were then tested with actual and hypothetical data. The results of the study showed that the networks can determine relationships between process parameters and the end product quality. It was also shown that the networks can be used to predict the effect on product quality from changes in process parameters. Additional work is in progress to create a larger data set for training over a broader region of the operating envelope. The result of this ongoing work will provide greater reliability in network prediction.