Relationship Between Grain Size And Volume Fraction Of Second Phase On Mechanical Properties Of AZ80 Magnesium Alloy

Magnesium alloys,as the lightest metal structural materials,play an important role in the fields of national defense,military,aerospace and electronic communications.AZ magnesium alloy is the earliest and most widely used magnesium alloy in all kinds of commercial magnesium alloys.However,the beta phase at the grain boundary of magnesium alloy directly destroys the continuity of the metal,and it is easy to form stress concentration or crack damage in the subsequent plastic forming process,thus shortening the fatigue life and decreasing the mechanical properties of magnesium alloy products.In theory,solid solution heat treatment and second phase precipitation strengthening can greatly improve the properties of magnesium alloysIn this paper,heat treatment experiments such as solid solution treatment and aging treatment have been carried out.Through metallographic microscope observation,calculation of grain size and volume fraction of the second phase,XRD diffraction analysis,tensile test and Brinell hardness measurement,the following conclusions are drawn?1?The tensile strength of AZ80 magnesium alloy increases with the decrease of grain size,the elongation increases with the increase of grain size after fracture,and the hardness decreases with the increase of grain size.After Origin software mathematical fitting calculation,the fitted mathematical equation is Rm=-0.7817×d+342.4;A=0.1754×d+14.45;HB=-0.6043×d+85.42?2?The tensile strength of AZ80 magnesium alloy increases with the increase of the volume fraction of the second phase,and then tends to be stable.The elongation after fracture decreases with the increase of the volume fraction of the second phase,and then tends to be stable,and the hardness increases as the volume fraction of the second phase increases.After Origin software mathematical fitting calculation,the mathematical relationship after fitting is as follows:Rm=?336.1 ×?+1315?/??+4.418?;A=0.004×?²-0.39 × ?+20.39;HB=0.3589×?+72.46.?3?The tensile strength of AZ80 magnesium alloy increases with the decrease of grain size and the increase of volume fraction of the second phase;the elongation increases with the increase of grain size and the decrease of volume fraction of the second phase after fracture,and the hardness changes periodically with the decrease of grain size and the increase of volume fraction of the second phase after breaking,and the hardness changes periodically with the increase of grain size and volume fraction of the second phase.The fitted number is calculated by Origin software.The academic relationship is as follows:Rm=(Z₀+A₀₁×?+B₀₁×d+B₀₂× d²+B₀₃ ×d³)/?1+A₁×?+A₂×?² +A₃ ×?³ +B₁× d+B₂ × d²?,?? Z₀=30.23,A₀₁=3.34,B₀₁=51.07,B₀₂=-2.24,B₀₃=0.021,A₁=0.006,A₂=0.0002,A₃=-0.000002,B₁=0.042,B₂=-0.002;A=Z₀+a× ?+b×d+c×d²+d₀×?²,?? Z₀=22.54,a=-0.4,b=-0.07,c=0.003,d₀=0.00 1;HB=Z₀+acos??/w1?+bsin??/w1?+c cos?d/w2?+d₀ sin?d/w2?,??Z₀=13 2.7,a=-5.36,b=4.54,c=-43.6,do=-30.8,w1=7.8,w2=27.8.?4?When aging temperature is lower than 140?,the second phase mainly precipitates in the discontinuous way near the grain boundary.When aging temperature is lower than 160?,the continuous precipitation in the grain boundary and the discontinuous precipitation at the grain boundary occur simultaneously.When aging temperature is higher than 180?,the second phase at the grain boundary gathers rapidly and extends to the grain boundary.?5?AZ80 magnesium alloy has the best solid solution effect when the solution temperature is 430? and the solution time is 5 h.The tensile strength is 323.21 MPa,the hardness is 68.76HB,and the elongation after fracture is 20.08%.After aging treatment,the tensile strength reaches 344.4 MPa,the hardness reaches 86.63 HB,and the elongation after fracture is reduced to 10.3%.