EFFECT OF FRICTION STIR PROCESSING ON CORROSION BEHAVIOR OF CAST AZ91C MAGNESIUM ALLOY

The corrosion behavior of as-cast AZ91C magnesium alloy was studied by performing friction stir processing (FSP) and FSP followed by solution annealing and then aging. Phase analysis, microstructural characterization, potentiodynamic polarization test and immersion tests were carried out to relate the corrosion behavior to the samples microstructure. The microstructural observations revealed the breakage and dissolution of coarse dendritic microstructure as well as the coarse secondary [Formula: see text]-Mg[Formula: see text]Al[Formula: see text] phase which resulted in a homogenized and fine grained microstructure (15[Formula: see text][Formula: see text]m). T6 heat treatment resulted in an excessive growth and dispersion of the secondary phases in the microstructure of FSP zone. The potentiodynamic polarization and immersion tests proved a significant effect of both FSP and FSP followed by T6 on increasing the corrosion resistance of the cast AZ91C magnesium alloy. Improve in corrosion resistance after FSP was attributed to grain refinement and elimination of segregations and casting defects which makes more adhesive passive layer. Increase in volume fraction of precipitations after T6 heat treatment is determined to be the main factor which stabilizes the passive layer at different polarization values and is considered to be responsible for increasing the corrosion resistance.

Effects of multi-pass FSP on the β phase (Mg17Al12) distribution and mechanical properties of AZ91C magnesium alloy

Purpose: The principle and advantages of friction stir processing (FSP) for the production of a highly formable Mg alloy, and some convincing experimental results are reported in this paper. The aim is to understand the relationship between the microstructure characteristics and the mechanical properties behaviour of the number of FSP passes AZ91C alloy. Design/methodology/approach: FSP is a solid state processing technique which involves plunging and traversing a square pin profiles FSP tool through the material. In this study, a fine-grained multi-phase AZ91C magnesium alloy was produced by applying FSP on as-cast AZ91C alloy. Findings: FSP achieved grain refinement and homogenization of the as-cast microstructure in Mg alloy AZ91C. FSP produced a fine homogeneous microstructure having a grain size of 6 μm throughout the plate. Also tensile properties of the specimen produced in one, two and three passes were investigated by standard tensile test. Results show that FSP improved the tensile characteristics of the as cast AZ91C alloy significantly. As the number of passes increased, higher UTS and TE were achieved due to finer grains and more dissolution of β phase (Mg17Al12). Originality/value: The present study shows that FSP is an efficient production method for a large-scale plate of a highly formable Mg alloy.