  Using a new numerical code we have carried out two-dimensional simulations of
the nonlinear evolution of unstable sheared magnetohydrodynamic flows. We
considered two cases: a strong magnetic field (Alfven Mach number, M_a = 2.5)
and a weak field (M_a =5). Each flow rapidly evolves until it reaches a nearly
steady condition, which is fundamentally different from the analogous
gasdynamic state. Both MHD flows relax to a stable, laminar flow on timescales
less than or of the order of 15 linear growth times, measured from saturation
of the instability. That timescale is several orders of magnitude less than the
nominal dissipation time for these simulated flows, so this condition
represents an quasi-steady relaxed state. The strong magnetic field case
reaches saturation as magnetic tension in the displaced flow boundary becomes
sufficient to stabilize it. That flow then relaxes in a straightforward way to
the steady, laminar flow condition. The weak magnetic field case, on the other
hand, begins development of the vortex expected for gasdynamics, but that
vortex is destroyed by magnetic stresses that locally become strong. Magnetic
topologies lead to reconnection and dynamical alignment between magnetic and
velocity fields. Together these processes produce a sequence of intermittent
vortices and subsequent relaxation to a nearly laminar flow condition in which
the magnetic cross helicity is nearly maximized. Remaining irregularities
consist of a pair of flux tubes straddling the shear layer. Fluctuations within
those features are closely aligned, representing Alfv\'en waves propagating
locally downstream.
