Material Evaluation Framework of Additive Manufactured Aluminum Alloys for Space Optical Instruments

Abstract

A framework for additive manufacturing aluminum alloy selection was developed to determine the preferred composition and process parameters from which to fabricate topology-optimized optical instrument housings and light-weighted freeform mirrors for the Compact Hyperspectral Air Pollution Sensor (CHAPS). In recent years, a number of high-strength laser powder bed fusion aluminum alloys have become commercially available, which are attractive for aerospace applications due to their high specific strength. Three aluminum alloys were selected for a three-Round experimental comparison. Each Round used a down-selected subset of alloys and parameter sets (candidates) from the previous Round. Round 1 screened a wide range of laser parameter sets for those that produced the highest density and tensile yield strength. Round 2 evaluated build quality using test geometries representative of CHAPS and assessed compatibility with post-processing, including optically black coating for the optical housings and nickelphosphorus plating for the mirrors. Round 3 characterized anisotropy in tensile and thermal properties. A rating system was developed which involved assigning priority weighting for CHAPS-specific criteria and binning test results into scoring categories to give a comparison score for each candidate which was used in the down-selection between Rounds. The framework selection process enabled a comparison of the relative strengths and weaknesses of each candidate and resulted in the selection of Scalmalloy as the preferred alloy for CHAPS. The selected candidate was used to develop design allowables for the topology optimization of CHAPS prototype housings, which were then fabricated.