Single-crystal ternary wurtzite Al0.8In0.2N thin films were grown epitaxially onto lattice-matched (111)-oriented Ti0.2Zr0.8N seedlayers. The epilayers were grown onto single-crystal MgO (111) substrates by magnetron sputter epitaxy (MSE) using reactive direct current magnetron sputtering in an N2 discharge under ultra-high-vacuum conditions. The growth temperatures ranged from 20 to 700 oC. Low-energy ion-assisted growth conditions, enhancing the epitaxy, were achieved by applying a negative substrate potential of 15-45 V. Film compositions and lattice parameters were determined using Rutherford Backscattering Spectroscopy (RBS) and High-Resolution X-ray diffraction (XRD), respectively. Cross-sectional High-Resolution Electron Microscopy of the interface regions verified the epitaxy and the crystallinity of the films. XRD ω-rocking scans of the Al0.8In0.2N 0002-peak showed full-width-at-half-maximum values of ~2400 arcs, indicating a high structural quality of the films. Opto-electronical properties were studied by cathodoluminescence at temperatures between 5 and 293 K. Luminescence was observed at wavelengths as short as 248 nm, corresponding to an energy of 5.0 eV. These results point towards the feasibility of metastable Al0.8In0.2N solid solutions as an active luminous material in opto-electronics. It also shows that MSE-grown Al0.8In0.2N can be an excellent choice for lattice-matched GaN heterostructures, with a resulting energy band-gap difference enabling strong charge carrier confinement. In addition to these new and original results, a brief review of the present work on Al(1-x)InxN growth at Linkoeping University is presented.