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Surface and interior precipitations of Mg 6 massAl alloy were morphologically studied by SPM observation with AFM and KFM modes, TEM and XRD methods. The hardness increment due to the precipitation was negligibly small. According to AFM contrast the precipitates on the surface were identiˆed as droplet-like particles (1～4 mm); on the other hand the ones formed in the alloy as needle-like (～1 mm). It was conˆrmed by XRD that both types of the precipitates had g structure (Al 12 Mg 17 ), and the peak height of the surface precipitates was about 3 times as high as that of the interior ones. The droplet-like precipitates projecting from the surface had a higher KFM electric potential than that of the matrix solid solution, however the precipitates embedded in either the surface layer or the matrix had a lower KFM electric potential.

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Keywords: be-ta type titanium alloy , omega phase, deformation mode, twinning boundary TEM specimen preparation: electropolishing (electrolyte; 6%HC1O4 , 35%Butanol, 59%CH3OH, 20 V, 223 K) TEM-utilized: Topcon EM-002B (200 kV)