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解理断裂通常发生在体心立方金属和密排六方金属,面心立方的铝合金极少发现解理断裂。通过OM、SEM和EDS等分析方法和冲击试验研究了Si对铸态多组元Al-5Mg-Mn-Cr-Ti焊料断裂韧性损失,着重研究了Si致焊料解理断裂机制。研究发现,当Si含量大于0.5%时面心立方的铝镁焊料中有解理断裂。随焊料中Si含量的增加,Mg2Si金属间化合物相增加,Mg2Si在晶界析出。Mg2Si相室温延展率几乎为零,硬度达450HV,存在严重的室温脆性。焊料晶粒边界存在的Mg2Si相在应力作用下开裂形成初生裂纹,初生裂纹形成后扩展到相邻α-Al晶粒,α-Al发生断裂,该断裂属于裂纹形核控制断裂。同时Si聚积在α-Al密排面(111)面上,弱化密排面原子结合力,断裂沿α-Al密排面扩展。Si含量从0.15%增加到0.8%时焊料的冲击韧性急剧劣化,冲击功从35 J下降到14 J。断裂特征由延性断裂转变为脆性解理断裂为主的混合型断裂。Si增加,焊料断裂韧性损失严重,Si等于0.5%为焊料韧脆转变的临界点。
Cleavage cleavage usually occurs in body-centered cubic metal and in close-packed hexagonal metal, and face-centered cubic aluminum found few cleavage fractures. The fracture toughness of Si multi-component Al-5Mg-Mn-Cr-Ti solder was investigated by means of OM, SEM and EDS analysis and impact test. The mechanism of Si-induced solute cleavage and fracture was also studied. The study found that when the Si content is greater than 0.5%, face-centered cubic aluminum-magnesium solder cleavage fracture. With the increase of Si content in the solder, Mg2Si intermetallic compound phase increases, Mg2Si precipitates at the grain boundary. The elongation at room temperature of Mg2Si phase is almost zero, the hardness reaches 450HV, there is a serious room temperature brittleness. The Mg2Si phase existing at the grain boundary of the solder cracks under the action of stress to form a primary crack. After the primary crack is formed, it expands to the adjacent α-Al grains and α-Al breaks down, and the fracture belongs to the crack nucleation controlled fracture. At the same time, Si accumulates on the (111) surface of α-Al close-packed surface, which weakens the atomic binding force of close-packed surface. The fracture expands along the dense surface of α-Al. The impact toughness of the solder deteriorates sharply as the Si content increases from 0.15% to 0.8%, and the impact energy drops from 35 J to 14 J. The fracture characteristics change from ductile fracture to brittle cleavage fracture. Si increases, the loss of fracture toughness of the solder is serious, and Si is equal to 0.5%, which is the critical point for the transition from ductile to brittle.