  We analyse a set of galaxy interactions performed by using a self-consistent
chemo-hydrodynamical model which includes star formation, Supernova feedback
and chemical evolution. In agreement with previous works, we find that
tidally-induced low-metallicity gas inflows dilute the central oxygen abundance
and contribute to the flattening of the metallicity gradients. The
tidally-induced inflows trigger starbursts which increase the impact of SN II
feedback injecting new chemical elements and driving galactic winds which
modulate the metallicity distribution. Although $\alpha$-enhancement in the
central regions is detected as a result of the induced starbursts in agreement
with previous works, our simulations suggest that this parameter can only
provide a timing of the first pericentre mainly for non-retrograde encounters.
In order to reproduce wet major mergers at low and high redshifts, we have run
simulations with respectively 20 and 50 percent of the disc in form of gas. We
find that the more gas-rich encounters behave similarly to the less rich ones,
between the first and second pericentre where low-metallicity gas inflows are
triggered. However, the higher strength of the inflows triggered in the more
gas-rich interactions produces larger metal dilutions factors which are
afterward modulated by the new chemical production by Supernova. We find that
the more gas-rich interaction develops violent and clumpy star formation
triggered by local instabilities all over the disc before the first pericentre,
so that if these galaxies were observed at these early stages where no
important tidally-induced inflows have been able to develop yet, they would
tend to show an excess of oxygen. We find a global mean correlation of both the
central abundances and the gradients with the strength of the star formation
activity. [abridged]
