The internal Mg diffusion (IMD) process is a promising method to fabricate MgB₂ wires because it produces a high-density MgB₂ layer with great intergrain connectivity. We have fabricated 100 m-class long 6+1-filament MgB₂ wires with high critical current densities using an IMD process. The MgB₂ layer and the sub-filament region are regular. The engineering critical current density(J_e) and MgB₂ fill factor of MgB₂ wires were improved obviously. The effect of high temperature treatment by conventional furnace annealing and rapid thermal processing on the superconducting properties and microstructure of IMD wire was also investigated. A best layercritical current density(J_c) and J_e as high as 2.8×10⁵ A/cm² and 3.1×10⁴ A/cm² at 4.2 K and 6 T were obtained by rapid thermal processing in the continuous heat treatment furnace. The J_e is about 1.0×10⁴ A/cm² and 5.2×10³ A/cm² at 8 and 10 T, respectively. The obtained results show that the IMD wires with excellent superconductivity and mechanical property is suitable for practical applications.

Keywords: MgB2, superconducting properties, microstructure, internal Mg diffusion