Influence of solid-solution treatment on corrosion performance of cast AM50 magnesium alloy
It was investigated by quenching the AM50 magnesium alloy test samples in water after T4 treating (420 °C) for 24 h. Then both kinds of the test bars were immersed in 3.5 wt. % NaCl saturation Mg (OH) 2 aqueous solution for 0, 24 and 72 h. Then tensile tests were taken. The microstructure of the samples was analyzed by scanning electronic microscope and X-ray diffraction. The results show that though solid-solution treatment improved the corrosion residual strength of the cast AM50 magnesium alloy for 24h, the deeper corrosion pits developed on the heat-treatment samples on 72h caused more drop of the strength compare to the untreated samples. The solid-solution treatment and the extreme depth theoretical of corrosion pits effect together to the corrosion residual strength.
Influence of microstructure on the corrosion of diecast AZ91D
The corrosion of die cast AZ91D was studied and related to its microstructure. For comparison and to more fully understand the behaviour of die cast AZ91D, corrosion studies and microstructural examinations were also carried out using slowly solidified high purity AZ91, Mg-2%Al, Mg-9%Al, low purity magnesium and high purity magnesium. Corrosion was studied in 1N NaCl at pH 11 by (1) observing the corrosion morphology, (2) measuring electrochemical polarisation curves and (3) simultaneously measuring both the hydrogen evolution rate and the magnesium dissolution rate. The skin of die cast AZ91D showed better corrosion resistance than the interior. This is attributed to a combination of(1) a higher volume fraction of the beta phase, (2) a more continuous beta phase distribution around finer alpha grains, and (3) lower porosity in the skin layer than in the interior of the die casting. This study showed that the casting method can influence the corrosion performance by its influence on the alloy microstructure. (C) 1999 Elsevier Science Ltd. All rights reserved.
Laser (Nd:YAG) cladding of AZ91D magnesium alloys with Al + Si + Al2O3
Abstract The laser surface cladding of AZ91D magnesium alloy with Al + Si + Al 2 O 3 powders (in the wt.% ratio of 7:1:2) was investigated. Laser processing was carried out with a 5 kW Nd:YAG laser. The microstructure and phase analyses of the surface cladding layer were carried out; furthermore, the morphology of the cladding zone, volume fraction and distribution of the Si and Al 2 O 3 particles in the laser surface cladding layer were also investigated. The average microhardness of the surface layer was measured in detail as a function of laser parameters. Microhardness of the surface layer was significantly improved to as high as 210 HV 0.05 as compared to 60–70 HV 0.05 of the AZ91D substrate, and the average microhardness of the cladding layer of the composite surfaced specimen decreases with increasing of laser power. However, the rate of decrease is faster at lower power. Though the average microhardness of the surface cladding layer remains constant, there is a little fluctuation in the reading in some regions possibly, because of the random distribution of hard particles in the cladding layer. Finally, the proper processing parameter ranges for formation of a homogeneous microstructure and enhancement of microhardness for laser surface cladding of AZ91D with Al + Si + Al 2 O 3 were established.