Low-lying excited states of 46 Ar have been studied via inverse-kinematics proton scattering with a thick target. Coupled-channels calculations have been used to extract the deformation length of the 2 + 1 state. This result, combined with existing Coulomb excitation data, yields a ratio of the neutron-to-proton transition matrix elements of M n /M p = 1.19(25)N/Z, showing a departure from the proton dominance observed in the N = 28 isotones above 48 Ca. The status of the N = 28 shell below 48 Ca is discussed.