Liuyan Zhang

Improving in-vitro biocorrosion resistance of Mg-Zn-Mn-Ca alloy in Hank's solution through addition of cerium

Abstract Two kinds of Mg-Zn-Mn-Ca alloys with and without cerium were designed and fabricated. In-vitro degradation tests and electrochemical evaluations were carried out to compare their biocorrosion behavior in Hanks solution at 37 °C. After adding cerium, the continuous network distributed Ca 2 Mg 6 Zn 3 phases in Mg-2Zn-0.5Mn-1Ca alloy (Alloy I) were separated due to the emerging non-continuously distributed Mg 2 Ca phase and Mg 12 CeZn phase. This change led to corrosion acceleration of Mg matrix at the initial stage but also sped up the formation of compact corrosion products for Mg-2Zn-0.5Mn-1Ca-1.5Ce alloy (Alloy II), and therefore enhanced its biocorrosion resistance. Cerium containing Alloy II has the potential to be used as future biomaterials.

Improvement of pitting corrosion resistance for Al-Cu alloy in sodium chloride solution through equal-channel angular pressing

Abstract Significant corrosion resistance improvement was achieved in solid-solution treated (T4) Al-Cu alloy after severe grain refinement through equal-channel angular pressing. The bulk ultrafine-grained Al-Cu alloy with grain sizes of 200-300 nm has higher pitting potential (elevated by about 34 mV, SCE) and lower corrosion current density (decreased by about 3.88 µA/cm 2 ) in polarization tests than the as-T4 alloy, and increased polarization resistance (increased by about 5.7 kΩ·cm 2 ) in electrochemical impendence spectrum tests, along with alleviated corrosion damage in immersion tests. Two factors responds to the improved corrosion resistance of the alloy: the first is the refinement of residual θ -phase (Al 2 Cu) particles leading to the lower micro-galvanic currents and reduced susceptibilities to pitting corrosion, the second is the mass of strain-induced crystalline defects providing more nucleation sites for the formation of more volume fractions of stable oxide film.

Heat treatment of novel low-carbon multi-alloyed anti-wear marine steel

Abstract A low-carbon anti-wear steel, multi-alloyed with Si-Cr-Mn-Al-Ni-Mo-(Nb, RE), was designed for vane pumps of ships. The novel cast steel after various heat treatments was characterized by microstructure observations and mechanical properties measurement in order to achieve an optimal process correlated with good abrasive resistance for a long marine service. Differential scanning calorimetry and hardness analyses deduced a complete austenitizing temperature of 1 000 °C, based on the alloying element homogenization and defective structure elimination without grain coarsening. An optimal austempering process (austenitized at 1 000 °C, quick cooled for holding at 350 °C for 1.5 h and then air-cooled to room temperature) produced a uniform mixture structure of fine carbide-free aciculate bainites and few lath martensites, resulting in the tensile strength increase of 34% and impact toughness increase of 50% compared with that of the as-cast steel. The abrasive wheel tests show that the austempered steel has good wear resistance with a mass-loss rate of 170 mg/(km·cm 2 ) under applied load of 70 N in acidic slurry. The new grade steel (containing anti-corrosion elements of Cr and rare earth) can find wide application in marine engineering, with further enhanced comprehensive properties via melting process improvement.