COMPARATIVE STUDY OF THE INFLUENCE OF FLUX AND FLUXLESS PROTECTION ON THE CORROSION RESISTANCE OF AZ91D ALLOY CASTINGS
DOI:
https://doi.org/10.15407/plit2026.03.003Keywords:
high-pressure die casting, magnesium alloy AZ91D, fluxless technology, gas protection, corrosion resistance, microstructure, bimetallic radiator-convectorAbstract
The paper presents the results of a comparative study of the influence of the magnesium melt protection type (flux protection with the use of VI2 flux and fluxless gas protection based on a SO₂ + SF₆ mixture) on the corrosion resistance, microstructure, and mechanical properties of castings made of the AZ91D alloy obtained by high-pressure die casting on a hot-chamber machine. The expediency of transition from the traditional flux protection — which is a source of hygroscopic chloride inclusions and corresponding micro-galvanic corrosion sites — to a fluxless melt protection technology under a gas atmosphere isolating the melt mirror without contaminating the alloy with non-metallic inclusions is substantiated. The test methodology included accelerated climatic tests (4 cycles of 24 hours each) and long-term atmospheric tests of specimens with dimensions of 40×40×1 mm. The corrosion resistance was evaluated by gravimetric (K_grav, g/m²·h) and depth (P, mm/year) indicators, as well as by the conventional 10-point corrosion resistance scale for metals (terminology — according to DSTU EN ISO 8044:2018). The experimental data were processed by mathematical statistics methods; to establish the influence of the composition of the protective gas mixture, three series of experiments were carried out according to a 2³ full-factorial design matrix. It has been established that the application of fluxless gas protection leads to a substantial increase in corrosion resistance (K_grav decreases from 2.01 to 0.008 g/m²·h, P — from 10.3 to 0.04 mm/year), a decrease in gas content in the casting from 16 to 3 cm³/100 g, and an increase in the tensile strength from 196 to 265 MPa. Microstructural analysis confirmed the absence of non- metallic inclusions larger than 0.5 µm (within the resolution of optical microscopy) and the formation of an equiaxed fine-grained structure of the Al solid solution in Mg with a uniformly distributed γ-phase (Mg₁₇Al₁₂). The obtained results substantiate the transition of castings from the «completely unstable» group (10 points) to the «stable» group (4 points) of the corrosion resistance scale.
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