Influences of Ca and Y Addition on the Microstructure and Corrosion Resistance of Vacuum Die-Cast AZ91 Alloy

doi:10.1007/s40195-014-0101-z

Abstract

Abstract:

The influences of Ca and Y additions on the microstructure and corrosion resistance of vacuum die-cast AZ91 alloys were investigated by optical microscope, electron scanning microscope, weight-loss test, and electrochemical corrosion experiment. The results indicate that the Ca or Ca and Y additions refined the microstructure and decreased the amount of Mg₁₇Al₁₂ phase on grain boundaries in the alloys. Meanwhile, the addition of Ca and Y led to the formation of network Al₂Ca phase and rod-like Al₂Y phase, improved the corrosion resistance of AZ91 magnesium alloy. Compared with AZ91 alloy, the corrosion rate of AZ91–1.5Ca–1.0Y alloy was decreased to 16.2%, and its corrosion current density was dropped by one order of magnitude after immersion in 3.5 wt% NaCl solution for 24 h.

Key words: AZ91 alloy, Ca and Y, Corrosion resistance, Microstructure, Polarization curve

Feng Wang, Jibao Li, Jing Liu, Dan Lv, Pingli Mao, Zheng Liu. Influences of Ca and Y Addition on the Microstructure and Corrosion Resistance of Vacuum Die-Cast AZ91 Alloy[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(4): 609-614.

Figures/Tables 10

Table 1 Actual compositions of experimental alloys (wt%)

Alloy	Al	Zn	Ca	Y	Mg
AZ91	9.06	0.61	0	0	Bal.
AZ91–1.5Ca	8.86	0.57	1.38	0	Bal.
AZ91–1.5Ca–1.0Y	8.92	0.63	1.45	1.16	Bal.

Fig. 1 OM images of the three alloys: a AZ91; b AZ91–1.5Ca; c AZ91–1.5Ca–1.0Y

Fig. 2 SEM images of AZ91 alloy a, AZ91–1.5Ca alloy b, AZ91–1.5Ca–1.0Y alloy c. EDS results of Al2Ca phase d, Al2Y phase e

Fig. 3 XRD pattern of AZ91–1.5Ca–1.0Y alloy

Fig. 4 Comparing the corrosion rates of the three alloys after immersion in 3.5 wt% NaCl solution for different times

Fig. 5 Polarization curves of the three investigated alloys

Table 2 Tafel fitting results for polarization curves of the three alloys

Alloy	Corrosion potential (V)	Corrosion current (A/cm²)	Corrosion rate (g/(m² h))
AZ91	-1.54	2.044 × 10^-4	0.91
AZ91–1.5Ca	-1.52	1.2821 × 10^-4	0.57
AZ91–1.5Ca–1.0Y	-1.50	5.92 × 10^-5	0.26

Fig. 6 Macrographs of AZ91 a, AZ91–1.5Ca b, AZ91–1.5Ca–1.0Y, c alloys after immersion in 3.5 wt% NaCl solution for 12 h

Fig. 7 SEM image of AZ91–1.5Ca–1.0Y alloy after corrosion a, EDS result of the area denoted by the frame in a b

Table 3 EDS results of the matrix of different alloys

Alloy	Content in mass fraction (wt%)				Content in atomic fraction (at%)
Alloy	Mg	Al	Ca	Y	Mg	Al	Ca	Y
AZ91	95.42	4.58	–	–	95.85	4.15	–	–
AZ91–1.5Ca	98.24	1.58	0.17	–	98.46	1.43	0.11	–
AZ91–1.5Ca–1.0Y	96.69	3.09	0.22	–	97.04	2.80	0.16	–

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