Influence of Sn addition on microstructure and corrosion resistance of AS21 magnesium alloy

This study aims to investigate the influence of Sn addition on microstructure and corrosion properties of AS21 magnesium alloys. The AS21 alloys with 0, 0.5, 1 and 2 wt.% Sn additions were produced by low pressure die casting method. Microstructure characterizations were performed by optical and scanning electron microscopy. Corrosion properties of the alloys were examined by immersion and electrochemical corrosion tests in 3.5% NaCl solution. The microscopic results showed that AS21 alloy consisted of α-Mg, isolated β-Mg17Al12 and Chinese script type Mg2Si intermetallic phases. With increasing amount of Sn, the distribution of Mg2Si phase became more discrete and denser. After 2 wt.% Sn addition, a Sn-rich network structure formed throughout the microstructure and islands of Chinese script shape were made of shorter rods of Mg2Si phase. The constant immersion corrosion tests revealed that increasing Sn addition led to a continual decrease in the degradation of AS21 alloys, in which the corrosion rate of AS21 alloy was decreased by approximately 65% with 2 wt.% Sn addition. The electrochemical corrosion tests also showed that the corrosion resistance of AS21 alloy was gradually improved with increasing Sn content.

Effects of Cd and Sn on double-peak age-hardening behaviors of Al-Si-Cu-Mg cast alloys

The effects of trace elements Cd and Sn on precipitation process of Al-Si-Cu-Mg cast alloys were investigated in the present research.It is shown that the addition of Cd and Sn not only increases remarkably the aging peak hardness and reduces the time to reach aging peak,but also eliminates the double-aging-peak phenomenon which appears in Al-Si-Cu-Mg alloys.In Al-Si-Cu-Mg alloys the first aging peak corresponds to GP zones(especially GPⅡ) ,and the second one is caused by metastable phases.The obvious time interval of transition from GPⅡ to metastable phases associates with the double-aging-peak phenomenon.The results of DSC and TEM show that Cd/Sn elements suppress the formation of GPⅠzone,stimulate the formation of θ",θ' and θ phases,and then shorten remarkably the temperature intervals of each exothermic peak.Because the transition interval between GPⅡzone and metastable phases is shortened by Cd/Sn in Al-Si-Cu-Mg cast alloys,θ' phase coexists with θ" phase in matrix of ageing peak condition,which causes effective hardening on the alloys,and at the same time,eliminates the double-aging-peak phenomenon.

Distinct beneficial effect of Sn on the corrosion resistance of Cr-Mo low alloy steel

In this work,the beneficial effect of Sn addition on the corrosion resistance mechanism of Cr-Mo low alloy steel was studied.Results demonstrated that Sn improves the corrosion resistance of the steel matrix mainly by influencing the microstructural transformation.Sn addition and the synergistic effect of Sn,Cr,and Mo promote the formation of α-FeOOH,SnO_(2),SnO,Cr(OH)_(3),and molybdates,lead to the improved protection and stability of the rust layer.This synergistic effect also endows the inner rust layer with cation selectivity,preventing the further penetration of Cl-and inhibiting the localized corrosion of steel.