Influence of Cu addition on microstructure and hardness of near-eutectic Al-Si-xCu-alloys

The influence of Cu content on the microstructure and hardness of near-eutectic Al-Si-xCu（x = 2%,3%,4% and 5%） was investigated.After melting Al-based alloys with different Cu contents,alloys were cast in green sand molds at 690 °C and solidified.The solution treatment was performed at 500 °C for 7 h and then the specimens were cooled by water quenching.The samples were respectively aged at 190 °C for 5,10 and 15 h to observe the effect of aging time on the hardness of matrix.Also differential thermal analysis was used to obtain the transition temperature of the equilibrium phases at cooling rate of 30 K/min and to determine the effect of Cu content on the formation of quaternary eutectic phases and the melting point of-（Al） ＋ Si.The results show that as Cu content in the alloy increases,the hardness of matrix increases due to precipitation hardening,the melting point of -（Al） ＋ Si decreases and the amount of these eutectic phases increases,quaternary eutectic phase with melting point of 507 -C forms when Cu content is more than 2%.

Effects of zinc content on strength and wear performance of Al-12Si-3Cu based alloy

The effects of Zn content on strength and wear performance of Al-12Si-3 Cu alloy synthesized by gravity casting were systematically investigated.The microstructure and mechanical properties of the alloys were evaluated using OM,XRD,SEM as well as hardness,tension,compression and Charpy impact tests.Their dry sliding wear tests were carried out with a ball-on-disk tester.Microscopic examinations revealed that the microstructure of the base alloy consisted of theα(Al)dendrites,needle-type and coarse Si particles,and CuAl2(θ)phase.The addition of Zn to this alloy resulted in the formation ofα-solid solution phase and the increase of coarse Si particles.The hardness,yield,tensile and compressive strengths,elongation to fracture and impact toughness of the Al-12Si-3 Cu-Zn alloys increased with increasing Zn content,but tendency in the tensile and compressive strengths and ductility reversed after adding 1.5%-2%Zn.In addition,the friction coefficient and volume loss of the Al-12Si-3 Cu-Zn alloys decreased with increasing Zn content.The study showed that the addition of Zn to Al-12Si-3 Cu alloy can improve its potential applications as tribological material.

Influence of Cu content on microstructure and mechanical properties of thixoformed Al-Si-Cu-Mg alloys

The effects of Cu content on the microstructure and mechanical properties of thixoformed Al-6Si-xCu-0.3Mg(x= 3,4,5and 6,mass fraction,%) alloys were studied.The samples were thixoformed at 50%liquid content and several of the samples were treated with the T6 heat treatment.The samples were then examined by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive X-ray(EDX) spectroscopy and X-ray diffraction(XRD) analysis,as well as hardness and tensile tests.The results show that the cooling slope casting and thixoforming process promote the formation of very fine and well distributed intermetallic compounds in the aluminium matrix and the mechanical properties of the alloys increase considerably compared with the permanent mould casting.The results also reveal that as the Cu content in the alloy increases,the hardness and tensile strength of the thixoformed alloys also increase.The ultimate tensile strength,yield strength and elongation to fracture of the thixoformed heat-treated Al-6Si-3Cu-0.3Mg alloy are 298 MPa,201 MPa and 4.5%,respectively,whereas the values of the thixoformed heat-treated alloy with high Cu content(6%) are 361 MPa,274 MPa and 1.1%,respectively.The fracture of the thixoformed Al-6Si-3Cu-0.3Mg alloy shows a dimple rupture,whereas in the alloy that contains the highest Cu content(6%),a cleavage fracture is observed.

Influence of Mg addition and T6 heat treatment on microstructure,mechanical and tribological properties of Al-12Si-3Cu based alloy

The aim of the present study was to investigate the influence of Mg addition and T6 heat treatment on microstructure,mechanical and tribological properties of the Al-Si-Cu-Mg alloys.In this context,a series of Al-12Si-3Cu-(0.5-2.5)Mg(wt.%)alloys were produced by permanent mould casting,and then subjected to T6 treatment.Their microstructure and mechanical properties were investigated using OM,XRD,SEM,EDS along with hardness,tension,compression and Charpy impact tests.Dry sliding friction and wear properties of the alloys were studied using a ball-on-disk type tester.It was observed that the microstructure of as-cast Al-12Si-3 Cu-Mg alloys consisted of a(Al),Si,O-CuAb,0-Mg_(2)Si,0-AbMg_(8)Cu(2)Si_(6) and π-AhMg_(3)FeSi_(6) phases.T6 heat treatment gave rise to nearly spherodization of eutectic Si particles,formation of finer 0-CuAH and 0-Mg_(2)Si precipitates and elimination of Chinese script morphology of 0-Mg_(2)Si phase.The addition of Mg up to 2.5 wt.%decreased the hardness,tensile and compressive strengths,tensile elongation and impact toughness of the as-cast and T6-treated alloys and increased their friction coefficient and volume loss.T6 treatment,on the other hand,led to a significant increase in mechanical properties and wear resistance of as-cast alloys.

Effect of Si content on laser welding performance of Al-Mn-Mg alloy

The correlation between Si content （0.1%-0.5%, mass fraction） and pulse laser welding performance of AI-Mn-Mg aluminum alloy sheets was studied. The sheets were fabricated in the laboratory, with gauge of 0.45 mm, H16 temper by pulse laser welding. It was found that no cracking existed in the welding pool as Si content was below 0.34%. However, when the Si content increased to 0.47%, cracking formed in the welding pool. Microstructure observations indicated that residual eutectic phases distributed at the grain boundaries were discontinuous and appeared to be small particles in lower Si content alloys; the residual eutectic phases distributed at the grain boundaries were partially continuous and appeared to be films in higher Si content alloys. These phenomena could explain why Si content adversely affected the laser welding performance.

Yield strength prediction of rolled Al-(1.44-12.40)Si-0.7Mg alloy sheets under T4 condition

The effects of Si content on the microstructure and yield strength of Al-(1.44-12.40)Si-0.7 Mg(wt.%)alloy sheets under the T4 condition were systematically studied via laser scanning confocal microscopy(LSCM),DSC,TEM and tensile tests.The results show that the recrystallization grain of the alloy sheets becomes more refined with an increase in Si content.When the Si content increases from 1.44 to 12.4 wt.%,the grain size of the alloy sheets decreases from approximately 47 to 10μm.Further,with an increase in Si content,the volume fraction of the GP zones in the matrix increases slightly.Based on the existing model,a yield strength model for alloy sheets was proposed.The predicted results are in good agreement with the actual experimental results and reveal the strengthening mechanisms of the Al-(1.44-12.40)Si-0.7 Mg alloy sheets under the T4 condition and how they are influenced by the Si content.

Al/Si对镍基合金在超临界水中腐蚀行为的影响

研究了4种不同Al/Si含量的Ni-Fe-Cr合金在700℃/25 MPa超临界水环境中的高温氧化行为,揭示了合金的氧化动力学、表面氧化膜组成及微观结构。结果表明,当Cr含量达到25%(质量分数)时,Ni-Fe-Cr合金在超临界水中能够形成稳定的保护性Cr_2O_3膜,合金中Si含量的增加有助于保护性氧化膜的快速形成,而较低的Al含量无法提高保护性氧化膜的化学稳定性。