TECHNOLOGY AREA(S): Materials/Processes

ACQUISITION PROGRAM: PMA201 Precision Strike Weapons

OBJECTIVE: Develop an innovative additive manufacturing (AM) process to successfully produce 7000 series (e.g., 7075 and 7050) aluminum alloy components.

DESCRIPTION: Naval aircraft components are commonly produced with 7000 series (e.g., 7075 and 7050) aluminum alloys due to their weight, strength, and fatigue properties.� Current additive manufacturing (AM) methods fall short of successfully producing 7000 series aluminum alloys due to the reflective nature of the material.� In addition, current AM methods, lacking ideal thermal control, print inherently defective products with such issues as poor surface finish and high residual stresses.

During AM processing of aluminum, defects could arise due to thermal stresses and a "Hot Tearing" effect of the alloy during solidification when the component rapidly cools, going from a very high melting temperature to the machine�s environmental temperature.� This high rate of cooling introduces large residual stresses that often deform the part being produced.� Microstructural issues such as residual porosity and rough surface finish are very common with current AM methods due to oxidation.

An innovative AM process is sought to successfully produce 7000 series aluminum alloy aircraft components.� The novel process should accurately control the thermal profile locally and globally during component fabrication and reduce defects due to oxidation.� Resulting components should demonstrate microstructural, mechanical and dynamic properties that are at least equivalent to, but preferably better than, traditionally produced parts and have minimal to no distortion per drawing tolerances.� An innovative AM process has the potential to improve operational readiness, reduce total ownership cost, and enable on-demand parts manufacturing for naval aviation.

PHASE I: Develop a proof of concept for a novel AM process for use with 7000 series aluminum alloys.� Demonstrate its feasibility to process 7000 series AM aluminum alloys to address defects (e.g., porosity, hot tearing, residual stress, and microstructural issues).� The Phase I effort will include prototype process plans to be developed during Phase II.

PHASE II: Fully develop the novel AM process to fabricate a series of coupons and naval aircraft components.� Perform coupon level testing, in accordance with ASTM E8, to fully characterize the resulting mechanical properties and non-destructive inspection (NDI) to verify microstructural properties, such as grain size and orientation, achieved through the AM process.� Demonstrate the capability of printing geometrically accurate aircraft components with complex geometry, per pre-existing tolerances, and verified by a laser scan.

PHASE III DUAL USE APPLICATIONS: Fully develop an AM process to fabricate naval aircraft components that can be integrated into the fleet.� Conduct final component level testing to demonstrate the mechanical and microstructural properties of the AM components meet or exceed traditionally manufactured components. The process developed through this effort will improve the quality of additively manufactured 7000 series aluminum parts.� The process will be directly applicable to a wide range of commercial applications, due to the high amount of usage of 7000 series aluminum in the commercial/private aerospace industry.� The proposed process will allow industry to apply the benefits of AM technology to many critical aircraft components.

REFERENCES:

1. Ruettimann, C., Bartlome, R., and Dury, N. �Reproducible Copper Welding.� Industrial Laser Solutions for Manufacturing, September/October 2013. http://www.industrial-lasers.com/articles/print/volume-28/issue-5/features/reproducible-copper-welding.html

2. Griffith, M.L., Keicher, D.M., Atwood, C.L., Romero, J.A., Smugeresky, J.E., Harwell, L.D., and Greene, D.L. �Free Form Fabrication of Metallic Components using Laser Engineered Net Shaping (LENS).� Proceedings of the Solid Freeform Fabrication Symposium, August 12-14, 1996, Austin, TX, p. 125. https://www.osti.gov/scitech/biblio/366460

3. Rubenchik, A., Wu, S., Mitchell, S., Golosker, I., LeBlanc, M. & Peterson, N. �Direct measurements of temperature-dependent laser absorptivity of metal powders.� Applied Optics, August 2015. https://www.osapublishing.org/ao/abstract.cfm?uri=ao-54-24-7230

4. Hendriks, A. & Naidoo, D. �The generation of flat-top beams by complex amplitude modulation with a phase-only spatial light modulator.� University of KwaZulu-Natal, 2012. http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1380168

5. Okunkova, A. and Volosova, M. �Experimental approbation of selective laser melting of powders by the use of non-Gaussian powder density distributions.� Moscow State University of Technology, 2014. http://www.sciencedirect.com/science/article/pii/S1875389214002405?via%3Dihub

6. ASTM E8 / E8M-16a, Standard Test Methods for Tension Testing of Metallic Materials, ASTM International, West Conshohocken, PA, 2016, www.astm.org/standards/E8.htm

KEYWORDS: Additive Manufacturing; High Strength Aluminum; Part Quality; Residual Strength Mitigation; Surface Reflectivity; Cost Reduction