New Reference Radiographs for Magnesium Alloy Castings

Abstract With the introduction and increased use of magnesium alloys containing zirconium, rare earth metals, and thorium, predominantly in castings for aircraft and spacecraft applications, it became evident that the existing reference radiographs included in ASTM E 155-64 would require updating to include radiographs for discontinuity types peculiar to these alloys. AFS Committee 2-D was assigned to undertake this project in cooperation with ASTM Section E07.02.02, which was reactivated for that purpose. Attempts to collect a suitable range of samples for specific reference radiographs from rejected production castings were unsuccessful, and it became obvious that these samples would have to be produced artificially. The metallurgical structure and characteristics of various discontinuities and their radiographic appearance are described. The discontinuity types examined were the following: graded series—(1) eutectic segregation—microshrinkage type, (2) gravity segregation—Zr, Mn, and (3) reacted sand inclusions; and single examples, for identification purposes only—(1) eutectic segregation—hot-tear type, (2) eutectic segregation—pipe-shrink type, and (3) flow line—eutectic depletion.