Biomedical Engineering Reference
In-Depth Information
pure Mg was still weak, in which the yield strength was 21MPa,UTS was 101MPa and the
elongation was 6.9%. With the increasing of Zn contents, the yield strength , UTS and the
elongation was increased. When the Zn content was up to 4.0wt.%, the mechanical
properties reach to the peak value, the yield strength was 58.1MPa, UTS was 216.85MPa
and the elongation was 15.8%. The mechanical properties of Mg-Zn binary alloy when
ulteriorly increasing of Zn contents was declined. Its UTS was 182 MPa, and its elongation
was only 7.2 % for Mg-6.0 Zn alloy. Direct estimation of stacking fault energy by
thermodynamic calculations showed that Zn reduces stacking fault energy of the Mg-Zn
alloys. Stacking fault energy is an important physical properties of the material, which
directly affects the mechanical properties, dislocation cross slip, phase stability and the
dynamic recrystallization of metal materials. It has been confirmed that the stacking fault
energy in magnesium alloy plays an important role in mechanical properties and the
dynamic recrystallization[22]
Alloy
Yield strength(MPa)
UTS (MPa)
Elongation (%)
Mg-1.0Zn
20±2
101.5±3
6.96±0.5
Mg-2.0Zn
27±2
145.9±5
12.23±1.5
Mg-3.0Zn
47±1.5
167.8±10
13.7±1.0
Mg-4.0Zn
58±1.0
216.8±15
15.8±5.5
Mg-5.0Zn
68±1.5
185±5
9.2±0.5
Mg-6.0Zn
69±1.5
182±5
7.2±0.5
Table 3. Mechanical properties of Mg-xZn alloys at room temperature
3.2.2 The effects of Ca content on mechanical property of the as-cast alloys
The tensile strength and elongation of as-cast Mg-4.0 Zn-x Ca alloys were shown in table 4.
The typical stress-train curves of as-cast Mg-4.0 Zn-x Ca alloys were depicted in Fig.6. The
ultimate tensile strength (UTS) and elongation of as-cast Mg-4.0 Zn alloy were 180MPa and
9.5%, respectively. After 0.2 wt. % Ca was added, the UTS and elongation of as-cast Mg-4.0
Zn-0.2 Ca alloy were improved to 215 MPa and 17.5%, respectively. When 0.5 wt. % Ca was
added, the Mg-4.0 Zn-0.5 Ca alloy has similar mechanical property as the Mg-4.0 Zn-0.2 Ca
alloy. However, the mechanical properties of as-cast Mg-4.0 Zn-1.0 Ca alloy began to
decline. When the Ca concentration was up to 2.0 wt. %, the alloy showed worse mechanical
property, its UTS was 142 MPa and elongation was only 1.7 %.
Fig.7 showed the typical fracture surfaces of as-cast Mg-4.0 Zn-x Ca alloys. As it was
showed that the fracture type was ductile fracture when Ca concentration was lower than
0.5 wt. %. Big dimples and tearing edges can be evidently observed on the fracture surface
of the as-cast Mg-4.0 Zn-0.2 Ca (Fig.8 (a)).When the Ca concentration was 1.0 wt. %, the Mg-
4.0 Zn-1.0 Ca alloy showed mixture fracture morphology. When the Ca concentration was
up to 2.0 wt. %, the fracture type of the alloy was brittle fracture. The
pearl-shaped
fracture
can be easily observed on the fracture surface of the as-cast Mg-4.0 Zn-2.0 Ca alloy
(Fig. 5 (c)).
