ValAx instead of CatAx should be used for scatter chart.

src/xlsx/xlsxchart.cpp

@@ -462,7 +462,7 @@ void ChartPrivate::saveXmlScatterChart(QXmlStreamWriter &writer) const
         saveXmlSer(writer, seriesList[i].data(), i);
 
     if (axisList.isEmpty()) {
-        const_cast<ChartPrivate*>(this)->axisList.append(QSharedPointer<XlsxAxis>(new XlsxAxis(XlsxAxis::T_Cat, XlsxAxis::Bottom, 0, 1)));
+        const_cast<ChartPrivate*>(this)->axisList.append(QSharedPointer<XlsxAxis>(new XlsxAxis(XlsxAxis::T_Val, XlsxAxis::Bottom, 0, 1)));
         const_cast<ChartPrivate*>(this)->axisList.append(QSharedPointer<XlsxAxis>(new XlsxAxis(XlsxAxis::T_Val, XlsxAxis::Left, 1, 0)));
     }