N141-062 TITLE: Aluminum Alloy Development and Use in Additive Manufacturing Process Design for Drive System Gear Boxes

TECHNOLOGY AREAS: Air Platform, Materials/Processes

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OBJECTIVE: Develop, optimize and then demonstrate the use of an optimizable aluminum alloy composition and associated additive manufacturing process for the advanced fabrication of gear boxes, to exceed the mechanical and chemical properties of investment cast A357.

DESCRIPTION: Cast magnesium alloys are used extensively in the fabrication of helicopter gear boxes because they are lightweight. Unfortunately, magnesium alloys have serious corrosion challenges and must be protected, inspected, and maintained via costly and time consuming sustainment procedures in order to ensure safe operation. Cast aluminum alloys are beginning to replace some magnesium castings because of their higher corrosion resistance. Unfortunately, industry has experienced challenges consistently producing the complex, quality aluminum casting needed with the strength and weight comparable to magnesium.

Additive manufacturing (AM), a process in which a part is fabricated layer by layer from a digital design package, offers the potential to produce complex components at reduced cost, and time. AM has the potential to conserve material, reduce energy consumption, part cost, and fabrication time. However, in order to use AM effectively, new aluminum alloys need to be developed that take advantage of the AM process in order to enhance strength and reduce weight.

To-date, only two traditional aluminum casting alloys have been used in the AM of aluminum components. However, these alloys were designed for casting operations in which alloy viscosity and elemental partitioning during solidification (10 deg/sec) must be minimized at the expense of strength, ductility, and fatigue resistance. A new class of alloys is needed to take advantage of the much faster cooling rates (>1000 deg/sec) and unique processing condition used during AM.

PHASE I: Demonstrate the feasibility of a new or optimized aluminum alloy composition for powder/feedstock material via an additive manufacturing process; focusing on alloy composition optimization for resulting initial mechanical properties (modulus, etc.) and effects on homogeneity and microstructure as a function of deposition and cooling rate.

PHASE II: Optimize, select, and demonstrate the full mechanical (strength, toughness, stiffness, modulus, etc.) and chemical (density, durability, galvanic, substrate and coating compatibility, etc.) properties for the new or optimized AM aluminum alloy composition(s); with the "as-cast" investment cast A357 as the baseline fabrication/processing and material property improvement, including relative cost/time to produce and sustain. Require demonstration of both static and fatigue strength of equivalent or superior performance to as-cast investment cast A357.

PHASE III: Transition alloy composition to commercial supply via OEM, bulk material vendors, or other partnering agreement. Demonstrate and transition AM process controls and settings to FRC and other DoD production/maintenance facilities.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Commercial aviation, automotive and industrial applications for advanced fabrication of lighter, stronger, more durable aluminum alloy drive system components via an AM process. Additional DoD transition opportunities in ground and amphibious vehicle components should also be pursued at this time if resulting properties and process requirements so warrant.

REFERENCES:
1. Frazier, W. "Direct Digital Manufacturing of Metallic Components: Vision and Roadmap" MAY 2010: USN Workshop - Direct Digital Manufacturing of Metallic Components: Affordable, Durable, and Structurally Efficient Airframes.

2. Herderick, E. "Additive Manufacturing of Metals" OCT 2011; Materials Science and Technology (MS&T) 2011.

KEYWORDS: Aluminum Alloy, Additive Manufacturing, Casting, Gearbox, Aircraft

** TOPIC AUTHOR (TPOC) **

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