壓鑄件抗蝕(shi)性(xing)差，當合金成(cheng)分中(zhong)雜質元素鉛、鎘、錫超過標準時，導致鑄件老化(hua)而發(fa)生變形(xing)，表現為(wei)(wei)體積脹大，機械性(xing)能特別是塑性(xing)顯著下降，時間長了甚至破(po)裂。鉛、錫、鎘在鋅合金中(zhong)溶解度(du)很小，因而集(ji)中(zhong)于(yu)晶(jing)粒邊(bian)界而成(cheng)為(wei)(wei)陰極，富(fu)鋁(lv)的固溶體成(cheng)為(wei)(wei)陽極，在水蒸氣(電(dian)解質)存在的條件下，促(cu)成(cheng)晶(jing)間電(dian)化(hua)學腐蝕(shi)。壓(ya)鑄件因晶(jing)間腐蝕(shi)而老化(hua)。

成(cheng)都(dou)陶瓷(ci)噴(pen)涂(tu)基(ji)(ji)準面(mian)選(xuan)(xuan)(xuan)擇要(yao)(yao)素，壓型(xing)型(xing)腔(qiang)尺(chi)寸檢查(cha)、鑄件(jian)(jian)(jian)劃線、機械(xie)加(jia)(jia)工(gong)(gong)(gong)都(dou)需要(yao)(yao)確定基(ji)(ji)準面(mian)。鑄件(jian)(jian)(jian)上的外(wai)圓、平面(mian)、內孔和(he)端面(mian)都(dou)可(ke)以作為基(ji)(ji)準面(mian)。合(he)適的基(ji)(ji)準面(mian)一(yi)般由設計、加(jia)(jia)工(gong)(gong)(gong)和(he)鑄造三(san)方面(mian)共同(tong)(tong)商(shang)定。選(xuan)(xuan)(xuan)擇基(ji)(ji)準面(mian)時一(yi)般應考慮下述各點：（1）熔模鑄件(jian)(jian)(jian)基(ji)(ji)準面(mian)一(yi)般選(xuan)(xuan)(xuan)擇非加(jia)(jia)工(gong)(gong)(gong)面(mian)，若(ruo)選(xuan)(xuan)(xuan)擇加(jia)(jia)工(gong)(gong)(gong)面(mian)時，是加(jia)(jia)工(gong)(gong)(gong)余量較少的面(mian)。（2）附(fu)件(jian)(jian)(jian)陶瓷(ci)噴(pen)涂(tu)基(ji)(ji)準面(mian)應選(xuan)(xuan)(xuan)擇與待加(jia)(jia)工(gong)(gong)(gong)面(mian)之(zhi)間(jian)有精(jing)度要(yao)(yao)求(qiu)的面(mian)，并盡量使零件(jian)(jian)(jian)的設計基(ji)(ji)準和(he)加(jia)(jia)工(gong)(gong)(gong)工(gong)(gong)(gong)藝基(ji)(ji)準重合(he)。（3）基(ji)(ji)準面(mian)的數目(mu)應約束六個(ge)(ge)自由度，故(gu)一(yi)般選(xuan)(xuan)(xuan)擇三(san)個(ge)(ge)基(ji)(ji)面(mian)（回轉體零件(jian)(jian)(jian)選(xuan)(xuan)(xuan)擇二個(ge)(ge)基(ji)(ji)面(mian)），并力求(qiu)劃線與加(jia)(jia)工(gong)(gong)(gong)為同(tong)(tong)一(yi)基(ji)(ji)面(mian)。

鋁鑄件裂紋的(de)產生(sheng)原因：1、鑄(zhu)件結構設計不(bu)合理，有尖(jian)(jian)角(jiao)，壁(bi)的(de)厚薄變化過于懸殊。如在這種情況下產生(sheng)裂痕的(de)應(ying)改(gai)進鑄(zhu)件結構設計，避免尖(jian)(jian)角(jiao)，壁(bi)厚力求均(jun)勻，圓滑過渡。2、砂(sha)型(xing)退(tui)讓性(xing)不(bu)良也(ye)(ye)會產生(sheng)裂紋。應(ying)采取(qu)增大砂(sha)型(xing)退(tui)讓性(xing)的(de)措(cuo)施(shi)。3、鑄(zhu)型(xing)局部過熱(re)會導致裂紋 ，應(ying)保證鑄(zhu)件各(ge)部分同時凝(ning)固或順序凝(ning)固，改(gai)進澆注系統設計。4、澆注溫(wen)度(du)(du)過高也(ye)(ye)會產生(sheng)裂紋，應(ying)適當降低澆注溫(wen)度(du)(du)。5、自鑄(zhu)型(xing)中(zhong)取(qu)出(chu)鑄(zhu)件過早會鑄(zhu)件變形(xing)時采用熱(re)校正(zheng)法應(ying)控(kong)制鑄(zhu)型(xing)冷(leng)卻(que)出(chu)型(xing)時間。6、熱(re)處(chu)理過熱(re)，冷(leng)卻(que)速度(du)(du)過激后產生(sheng)裂紋，鑄(zhu)件變形(xing)時采用熱(re)校正(zheng)法。正(zheng)確(que)控(kong)制熱(re)處(chu)理溫(wen)度(du)(du)，降低淬(cui)火冷(leng)卻(que)速度(du)(du)。

1)增大合金(jin)液(ye)的(de)(de)(de)冷卻速(su)度，如(ru)盡(jin)可能采(cai)用冷鐵、激冷砂(sha)(sha)乃至金(jin)屬(shu)型(xing)模;2)降低鋁(lv)(lv)液(ye)中的(de)(de)(de)氫含量(liang)(liang)(liang)(liang)及氧化(hua)鋁(lv)(lv)夾雜，如(ru)提(ti)高(gao)液(ye)態鋁(lv)(lv)的(de)(de)(de)熔(rong)化(hua)質(zhi)量(liang)(liang)(liang)(liang)，設置陶瓷(ci)過(guo)濾網，或增渦直接(jie)吊出(chu)作澆(jiao)包用;3)鋁(lv)(lv)壓(ya)鑄件(jian)將(jiang)熔(rong)化(hua)溫度控(kong)制(zhi)在750℃以下(xia)，并(bing)采(cai)用盡(jin)可能低的(de)(de)(de)澆(jiao)注溫度;4)將(jiang)鋁(lv)(lv)液(ye)的(de)(de)(de)變(bian)(bian)質(zhi)劑由易產生針孔缺陷(xian)的(de)(de)(de)鈉(na)鹽變(bian)(bian)成銻(ti)、啼等長效(xiao)變(bian)(bian)質(zhi)劑;5)在化(hua)學成分滿足(zu)ZLlolA型(xing)合金(jin)技(ji)術要求的(de)(de)(de)條件(jian)下(xia)，盡(jin)量(liang)(liang)(liang)(liang)降低鎂含量(liang)(liang)(liang)(liang)，適當提(ti)高(gao)硅含量(liang)(liang)(liang)(liang);6)選(xuan)擇(ze)含氣和(he)夾雜少、冶金(jin)質(zhi)量(liang)(liang)(liang)(liang)高(gao)的(de)(de)(de)鋁(lv)(lv)錠及其它原材料(liao)，回(hui)爐(lu)料(liao)(指廢鑄件(jian))的(de)(de)(de)加入(ru)量(liang)(liang)(liang)(liang)也應(ying)嚴(yan)(yan)格控(kong)制(zhi)在15%以下(xia);7)降低樹脂(zhi)砂(sha)(sha)型(xing)芯和(he)涂(tu)(tu)料(liao)的(de)(de)(de)發氣量(liang)(liang)(liang)(liang)，如(ru)嚴(yan)(yan)格將(jiang)樹脂(zhi)的(de)(de)(de)加入(ru)量(liang)(liang)(liang)(liang)控(kong)制(zhi)在1.0腸以下(xia)，再(zai)生砂(sha)(sha)添加一(yi)定比(bi)例的(de)(de)(de)新砂(sha)(sha)等;8)嚴(yan)(yan)格控(kong)制(zhi)涂(tu)(tu)料(liao)烘(hong)(hong)(hong)烤溫度，水基涂(tu)(tu)料(liao)的(de)(de)(de)烘(hong)(hong)(hong)烤溫度由150~1800C提(ti)高(gao)到180~200℃，烘(hong)(hong)(hong)烤時間不(bu)短(duan)于h2。烘(hong)(hong)(hong)干后(hou)，置放h8以上的(de)(de)(de)型(xing)芯應(ying)重新烘(hong)(hong)(hong)干;9)采(cai)取如(ru)底注式、大澆(jiao)口(kou)盆、開放式澆(jiao)注系(xi)統等各種(zhong)鑄造(zao)工藝措施，確保(bao)金(jin)屬(shu)液(ye)平穩(wen)充型(xing);10)保(bao)證壓(ya)鑄件(jian)和(he)砂(sha)(sha)芯排氣暢(chang)通，如(ru)設置出(chu)氣冒(mao)口(kou)，盡(jin)量(liang)(liang)(liang)(liang)將(jiang)暗冒(mao)口(kou)改成明冒(mao)口(kou)、扎(zha)出(chu)氣孔等。