The presented work is aimed to deal with the influence of changes in the value of negative (relative) pressure maintained in the die
cavity of pressure die casting machine on the surface quality of pressure castings. The examinations were held by means of the
modified Vertacast pressure die casting machine equipped with a vacuum system. Castings were produced for the parameters selected
on the basis of previous experiments, i.e. for the plunger velocity in the second stage of injection at the level of 4 m/s, the pouring
temperature of the alloy equal to 640°C, and the die temperature of 150°C. The examinations were carried on for three selected values
of negative gauge pressure: - 0.03, - 0.05, and - 0.07 MPa. The quality of casting was evaluated by comparing the results of the surface
roughness measurements performed for randomly selected castings. The surface roughness was measured by means of Hommel Tester
T1000. After a series of measurements it was found that the smoothest surface is exhibited by castings produced at negative gauge
pressure value of - 0.07 MPa.