  Superconducting Ag or Cu sheathed MgB2 wires have been fabricated by
conventional powder-in-tube techniques. The in-situ reaction of Mg and B
powders with atomic proportions of 1:2 and 1.33:2 inside Ag or Cu tubes at low
temperatures have been searched. An active alloying of Mg with Ag or Cu sheaths
at temperatures below 660 C has been observed. For Ag sheaths, there is a
strong diffusion of Mg, which does not allow the formation of large amounts of
MgB2 at the core. For Cu sheaths, the diffusion of Mg is stopped by the
formation of a MgCu2 layer around the superconducting core and an appropriated
excess of Mg leads to superconducting cores with Tc=39 K and good Jc values,
thus being possible the development of Cu/MgB2 composite wires.
