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This study aims to examine the variation in corrosion characteristics and tensile properties of WE43 magnesium alloy in an actual marine atmospheric environment by means of outdoor exposure tests. The macroscopic corrosion morphology, microstructure, and tensile properties were analyzed. The results indicated that WE43 alloy will corrode rapidly during exposure under marine atmospheric environmental conditions, resulting in a loose and porous Mg(OH)2 layer on the surface. The Mg matrix was mainly consumed as an anode, leading to the occurrence of corrosion pits. With the increase in exposure time, both the tensile strength and plasticity of WE43 alloy gradually deteriorated. After exposure for six months, the elongation and area reduction were significantly reduced, with a reduction ratio of more than 50%. After 18 months of exposure, the ultimate strength of the alloy decreased from 359 MPa to 300 MPa. According to an analysis of fractures in the alloy, the corrosion pits on the sample surface were the main reason for the decrease in tensile properties. [ABSTRACT FROM AUTHOR]

For the large magnesium alloy ingot, there is a considerable difference in cooling rate of different parts in the ingot, which leads to non-uniform distribution of the secondary phases, solute segregation and tensile properties. In the present research, an heavy AZ61 alloy ingot with a diameter of 500 mm was made by semi-continuous casting. The microstructure and mechanical properties at different positions along the radial direction of the large ingot were investigated by using an optical microscope (OM), a scanning electron microscope (SEM), an energy dispersive spectroscope (EDS), and a micro-hardness tester. The results indicate that the microstructure of the AZ61 ingot is non-uniform in different locations. It changes from equiaxed to columnar grains from the center to the edge; the average grain size gradually reduces from 1,005 μm to 763 μm, the secondary dendrite arm spacing reduces from 78 μm to 50 μm, and the Mg17(Al,Zn)12 phase is also refined. The micro-hardness value increases from 55.4 HV at the center to 72.5 HV at the edge of the ingot due to the microstructure differences, and the distribution of micro-hardness at the edge of the ingot is more uniform than that in the center. The tensile properties at room temperature show little difference from the center to the edge of the ingot except that the elongation at the edge is only 3.5%, much lower than that at other areas. The fracture mechanism is ductile fracture at the center and cleavage fracture at the edge of the ingot, and at the 1/2 radius of the ingot, a mixture of ductile and cleavage fracture is present.

To obtain a spheroidal microstructure of a semi-solid Mg-Zn-Nd-Zr alloy, which is favorable for the subsequent thixocasting process, the recrystallization and partial remelting (RAP) method was used in this study, and the microstructure evolution of the alloy and the mechanism of the shape factor change during the RAP process were invesigated. The as-cast Mg-Zn-Nd-Zr alloy was prepared in a metal mold and then extruded into bars with an extrusion ratio of 16:1. Partial remelting was carried out on the extruded samples at 589 ℃ (at a heating rate of 0.5 ℃·s-1) for different holding times ranging from 0 to 90 min. To examine the effect of heating rate, partial remelting of samples at the heating rate of 2 ℃·s-1 was also performed. Results show that the extruded microstructure rapidly evolutes into recrystallized grains in the semi-solid state; the liquid film initially forms at grain boundaries during the partial remelting, and then gradually changes from continuous into discontinuous state with the increase of holding time; this results in the agglomeration of adjacent grains and the decrease in shape factor. The value of shape factor increases continuously with holding time at first and reaches the maximum 0.62 when holding for 60 min, while decreases rapidly after a prolonged holding time. Moreover, local melting, mainly due to the inhomogeneous deformation during extrusion, becomes more significant and less uniformly distributed at a relatively higher reheating rate. The Mg-Zn-Nd-Zr magnesium alloy components have been thixo-cast successfully using the RAP method, which strongly proves the feasibility of RAP process in Mg-Zn-Nd-Zr alloy.

This study aimed to investigate the impact of corrosion on the microstructure and tensile properties of 7075 high-strength alloy. It involved outdoor exposure tests in an actual marine atmospheric environment in Wanning, Hainan Province. The results showed that the 7075 alloy was corroded rapidly in the marine atmospheric environment, and corrosion pits and intergranular cracks were generated. The intergranular cracks were extended along the grain boundary during corrosion, leading to the exfoliation of the matrix. The cause for the intergranular corrosion was discussed based on the microstructure characteristics of 7075 alloy. The tensile properties of the 7075 alloy gradually deteriorated with the increase of exposure time in the marine atmospheric environment. The ultimate strength and elongation were decreased by about 3.2% and 58.3%, respectively, after 12 months of outdoor exposure. [ABSTRACT FROM AUTHOR]

This work analyzed changes in the corrosion morphology and mechanical performance of 7085 aluminum alloy after outdoor exposures for different times in a humid and hot marine atmospheric environment. After one month of exposure, a pronounced corrosion of the alloy was observed. The corrosion product was mainly Al(OH)3, and the corrosion features were mainly pitting corrosion and intergranular corrosion (IGC). With the exposure time extended from 6 months to 12 months, the IGC depth increased from 114 μm to 190 μm. After a 1-year outdoor exposure in a humid and hot marine environment, the alloy's ultimate strength and yield stress remained nearly unchanged, while its elongation and area reduction decreased from the original 6% and 9%, respectively, to 3% and 5%. Moreover, the reasons for IGC and its effect on the mechanical performance was analyzed. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the corrosion behavior of 2xxx aluminum alloys in the marine environment and the degradation of mechanical properties caused by corrosion as well as to provide support for the lightweight design of marine equipment. The corrosion characteristics of 2297-T8 and 2195-T8 were observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) at 3, 6, 9, and 12 months of exposure, and the mechanical properties were obtained via uniaxial tensile testing. The results of the study showed the following: (1) With an increase in the exposure time, the corrosion products on the surface of 2297-T8 gradually increase, and the corrosion products on the surface of 2195-T8 accumulate rapidly. (2) The results of EDS show that the corrosion products of 2297 are mainly Al oxides and that those of 2195 are composed of Al, Fe, Mn, Si, etc. (3) Through the corrosion pit diameter, corrosion pit depth, and corrosion mass reduction rate surface, the trend of an increasing average radius of the corrosion pits and the corrosion mass reduction rate surface varies linearly, and the average depth of the corrosion pits increases dramatically after 9 months of exposure time. (4) According to the mechanical properties of the study surface, in a marine atmosphere, the degradation of 2297-T8 ductility is higher than that of 2195-T8, while the degradation of the yield stress is lower than that of 2195-T8. [ABSTRACT FROM AUTHOR]

Actual marine atmospheric pre-corrosion behavior and its effect on the fatigue performance of 7075-T73 aluminum alloy were studied by means of marine atmospheric outdoor exposure testing and fatigue testing. The surface and cross-sectional microstructures of aluminum alloy specimens after different numbers of days of exposure were analyzed. Localized pitting, and intergranular and exfoliation corrosion occurred during the outdoor exposure of aluminum alloy specimens in a marine atmosphere. The degree of severity of atmospheric corrosion increased with increasing duration of exposure. The effects of Fe-rich constituent particles (Al23CuFe4) and grain boundary precipitates (MgZn2) on the marine atmospheric corrosion behavior were discussed. In addition, when the exposure time was increased from 0 days to 15 days, the average fatigue life of aluminum alloy specimens decreased dramatically from about 125.16 × 104 cycles to 16.58 × 104 cycles. As the exposure time was further increased to 180 days, the average fatigue life slowly decreased to about 6.21 × 104 cycles. The fatigue fracture characteristics and the effect mechanism of marine atmospheric pre-corrosion on the fatigue life of 7075-T73 aluminum alloy were also analyzed. [ABSTRACT FROM AUTHOR]

To obtain a spheroidal microstructure of a semi-solid Mg-Zn-Nd-Zr alloy, which is favorable for the subsequent thixocasting process, the recrystallization and partial remelting (RAP) method was used in this study, and the microstructure evolution of the alloy and the mechanism of the shape factor change during the RAP process were invesigated. The as-cast Mg-Zn-Nd-Zr alloy was prepared in a metal mold and then extruded into bars with an extrusion ratio of 16:1. Partial remelting was carried out on the extruded samples at 589 °C (at a heating rate of 0.5 °C -s'1) for different holding times ranging from 0 to 90 min. To examine the effect of heating rate, partial remelting of samples at the heating rate of 2 °c-s~1was also performed. Results show that the extruded microstructure rapidly evolutes into recrystallized grains in the semi-solid state; the liquid film initially forms at grain boundaries during the partial remelting, and then gradually changes from continuous into discontinuous state with the increase of holding time; this results in the agglomeration of adjacent grains and the decrease in shape factor. The value of shape factor increases continuously with holding time at first and reaches the maximum 0.62 when holding for 60 min, while decreases rapidly after a prolonged holding time. Moreover, local melting, mainly due to the inhomogeneous deformation during extrusion, becomes more significant and less uniformly distributed at a relatively higher reheating rate. The Mg-Zn-Nd-Zr magnesium alloy components have been thixo-cast successfully using the RAP method, which strongly proves the feasibility of RAP process in Mg-Zn-Nd-Zr alloy. [ABSTRACT FROM AUTHOR]

Effects of actual marine atmospheric precorrosion and prefatigue on the fatigue property of 7085-T7452 aluminum alloy were investigated by using the methods of marine atmospheric outdoor exposure tests and constant amplitude axial fatigue tests. Marine atmospheric corrosion morphologies, fatigue life, and fatigue fractography were analyzed. After three months of outdoor exposure, both pitting corrosion and intergranular corrosion (IGC) occurred, while the latter was the dominant marine atmospheric corrosion mode. Marine atmospheric precorrosion could result in a dramatical decrease in the fatigue life of the as-received 7085-T7452 aluminum alloy, while selective prefatigue can improve the total fatigue life of the precorroded specimen. The mechanism of the actual marine atmospheric corrosion and its effects on the fatigue life of the 7085-T7452 aluminum alloy were also discussed. [ABSTRACT FROM AUTHOR]