. Typical cases of the deterioration of muntz metal (60:40 brass) by selective corrosion. . Fig. 2.—Micro structural changes induced in Muntz metal by dezincification (a) Unattacked Muntz metal (Fig. i, b). The light-colored matrix is the zinc-rich or /3 constituent, inwhich are embedded the finger-like crystals of the a. or constituent richer in (X500.) (6) Corroded Muntz metal. At the edge of the corroded portion (Fig. 1,6) the /S constituent has beenconverted into a porous mass of copper (black in the figure) which still retains its former shape. ( X 500.) Etching in both cases, am
. Typical cases of the deterioration of muntz metal (60:40 brass) by selective corrosion. . Fig. 2.—Micro structural changes induced in Muntz metal by dezincification (a) Unattacked Muntz metal (Fig. i, b). The light-colored matrix is the zinc-rich or /3 constituent, inwhich are embedded the finger-like crystals of the a. or constituent richer in (X500.) (6) Corroded Muntz metal. At the edge of the corroded portion (Fig. 1,6) the /S constituent has beenconverted into a porous mass of copper (black in the figure) which still retains its former shape. ( X 500.) Etching in both cases, ammonium hydroxide and hydrogen peroxide. 6 Technologic Papers of the Bureau of Standards It will be noted that the portion of the bolt which was mostdeeply corroded is that part which was subject to the greatestservice stresses (transverse bending). Although apparently thismaterial gave six years service, it should be borne in mind in. Fig. 3.—Arrangement of the Muntz metal bolts (type 1) in the keel of the boat The part which was most severely corroded corresponds to the portion most highly stressed (i. e., trans-versely) in service. comparing this case with the others described that the bolts werenot constantly bathed in sea water for this period and that theperiods of attack were intermittent, as illustrated by the con-centric lines in Fig. ib. Deterioration of Muntz Metal
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