PSI - Issue 19

Kiyotaka Masaki / Procedia Structural Integrity 19 (2019) 168–174

169

Kiyotaka MASAKI/ Structural Integrity Procedia 00 (2019) 000–000

2

structural components, many researchers investigate fatigue property of magnesium alloy. Since the examination of fatigue property requires a lot of time and cost, it is useful in design of mechanical components if there is a method that can estimate fatigue strength by a simple method. For example, in steel materials, the proportional relationship between fatigue limit and Vickers hardness of matrix, and the proportional relationship between fatigue limit and tensile strength are well known (Nishijima, 1980). If the same proportionality is established in Mg alloy, it is very useful information. On the other hand, in order to investigate the very high cycle fatigue property of three types of non-ferrous metals—die-cast aluminum, extruded magnesium and β-titanium alloys—, a research sub-committee on very high cycle fatigue has been established in the Society of Materials Science, Japan (Nakamura et al., 2017). In this research, as part of the research, rotating bending fatigue tests on three types of Mg-Al-Zn alloys was conducted and the correlation between static strength characteristics and fatigue limit was investigated.

Nomenclature  0.2T

the tensile 0.2 % proof stress the compressive 0.2 % proof stress

 0.2C  BT  BC

the tensile strength

the compressive strength

the elongation



the Young’s modulus



the first horizontal stress in the two-step bending S-N curve

 wh  w10  wL  w(est) 8

the fatigue strength at 10 8 cycles

the minimum stress at which test specimen fatigued

the estimated fatigue limit

2. Experimental procedure

2.1. Materials

Commercial general three types of extruded magnesium alloys —AZ31, AZ61 and AZ80 which were provided by Sankyo Tateyama, Inc. Sankyo Material-Company in JAPAN— were used for this study. Chemical compositions of these materials are shown in Table 1. No thermal treatment was applied to all of these materials. Fig.1 shows the microstructure of the materials. AZ31 is a mixed structure of small grain crystals and large grain crystals, whereas the crystal grain sizes of AZ61 and AZ80 were uniform. The average grain sizes of AZ31, AZ61 and AZ80 were

Table 1. Chemical composition of materials. [wt%] Material Al Zn Mn

Si

Fe

Cu

Ni

Mg Bal. Bal. Bal.

AZ31 AZ61 AZ80

3.0 5.9 8.1

1.1 0.6 0.5

0.31 0.28 0.25

0.007 0.010

0.002 0.002 0.002

0.001 0.002 0.002

0.001 0.002 0.001

0.38

a

b

c

100  m

Fig. 1. Micro structure of materials (a) AZ31; (b) AZ61; (c) AZ80.