喷射成形过共晶AlSiCuMg合金的固溶行为

Solution Behavior of Spray-Formed Hypereutectic AlSiCuMg Alloy

利用OM、XRD、SEM+EBSD、TEM、硬度测试以及相图计算研究了喷射成形Al25Si4Cu1Mg(质量分数,%)合金在固溶过程中的第二相和晶粒演变行为。结果表明:喷射成形过共晶AlSi合金的热挤压组织包含等轴状α-Al、微米级先共晶Si、非层片状共晶Si、共晶AlCuSiMg、共晶Al_(2)Cu相以及低体积分数的富Fe相。α-Al中还包含脱溶析出的微纳米和纳米级Al_(2)Cu相。Si相和α-Al的晶粒尺寸随固溶温度的升高而连续粗化。在475~495℃温度范围固溶时,脱溶相以及部分共晶Al_(2)Cu相随固溶温度的升高而回溶,残余Al_(2)Cu相向富Fe相聚集并粗化,AlCuSiMg相的体积分数和尺寸有所增加。515℃固溶时,第二相回溶程度继续提高,AlCuSiMg相的体积分数开始下降,但未见明显过烧现象。固溶温度超过515℃后,非平衡共晶相的熔化随温度的升高而加剧。过烧组织以晶界处的网状共晶和晶界宽化为主要特征。喷射成形Al25Si4Cu1Mg合金的硬度取决于溶质原子固溶度、残余第二相体积分数、α-Al晶粒尺寸、Si相尺寸以及非平衡共晶相熔化5个相互制约的因素。

Al-Si multicomponent alloys are commonly used in automotive and aerospace fields owing to their excellent castability,good wear resistance,and low coefficient of thermal expansion.After adding Cu and Mg followed by appropriate heating,AlCu,AlCuSiMg,or MgSi phases precipitate in anα-Al matrix.Hypereutectic AlSiCuMg alloys have been used in wear-resistant products,such as engine cylinders,pistons,and air-conditioning rotors,owing to the hardening effect of Si particles and the solid solution strengthening and precipitation strengthening effects of Cu and Mg.The evolution behaviors of secondary phases and the grains of the spray-formed Al25Si4Cu1Mg(mass fraction,%)alloy were examined via OM,XRD,SEM+EBSD,TEM,hardness tests,and phase diagram calculations.The results showed that the hot extrusion microstructure of spray-formed hypereutectic AlSi alloys comprises equiaxedα-Al,proeutectic Si,eutectic Si,eutectic AlCuSiMg,a eutectic AlCu phase,and a low volume fraction Fe-bearing phase at the micron level but without a lamellar morphology.α-Al contained both micro-nano and nano-sized AlCu phases precipitates.Over the temperature range of 475-495℃,the precipitated AlCu phase and some of the eutectic AlCu phase redissolved,and the residual AlCu phase concentrated to a Fe-bearing phase and coarsened.The volume fraction and size of the AlCuSiMg phase increased.However,when solution-treated at less than 515℃,the volume fraction of the AlCuSiMg phase began to decrease,and no overburning structure was observed.When the solution temperature exceeded 515℃,the incipient melting of the nonequilibrium eutectic phase increased with increasing solution temperature.The main characteristics of the overburning structure were the network eutectic and grain boundary broadening.The hardness of the spray-formed Al25Si4Cu1Mg alloy was dependent on five factors:the solid solubility of solute atoms,the volume fraction of the residual second phase,the grain size ofα-Al,the scale of the Si phase,and the incipient melting of the nonequilibrium eutectic phase.